Use these links to rapidly review the document
TABLE OF CONTENTS

Table of Contents

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of
the Securities Exchange Act of 1934 (Amendment No.          )

Table of Contents

Main Street Capital Corporation
1300 Post Oak Boulevard, Suite 800
Houston, Texas 77056

                                    , 2010

Dear Stockholder:

        You are cordially invited to attend this year's Annual Meeting of Stockholders of Main Street Capital Corporation, which will be held on June 10, 2010, at 1330 Post Oak Boulevard, First Floor Auditorium, Houston, Texas, commencing at 9:00 AM, local time. The notice of annual meeting and proxy statement following this letter describe the matters to be acted on at the meeting.

        If your shares are held in book-entry form on the records of American Stock Transfer & Trust Company, our transfer agent and registrar, we have enclosed a proxy card for your use. You may vote these shares by completing and returning the proxy card or, alternatively, calling a toll-free telephone number or using the Internet as described on the proxy card. If a broker or other nominee holds your shares in "street name," your broker has enclosed a voting instruction form, which you should use to vote those shares. The voting instruction form indicates whether you have the option to vote those shares by telephone or by using the Internet.

        Thank you for your support.

YOUR VOTE IS IMPORTANT.

Whether or not you plan to attend the meeting, please take a few minutes now to vote your shares.

Table of Contents

Important Notice Regarding the Availability of Proxy Materials for the Annual Meeting of Stockholders to Be Held on June 10, 2010.

        Our proxy statement and annual report on Form 10-K for the year ended December 31, 2009 are available on the Internet at http://mainstcapital.com under the "Proxy and Annual Report" section of our web site.

        The following information applicable to the Annual Meeting may be found in the proxy statement and accompanying proxy card:

•

The date, time and location of the meeting;



•

A list of the matters intended to be acted on and our recommendations regarding those matters;



•

Any control/identification numbers that you need to access your proxy card; and



•

Information about attending the meeting and voting in person.

Table of Contents

Main Street Capital Corporation
1300 Post Oak Boulevard, Suite 800
Houston, Texas 77056

NOTICE OF 2010 ANNUAL MEETING OF STOCKHOLDERS

        The 2010 Annual Meeting of the Stockholders of Main Street Capital Corporation, a Maryland corporation, will be held at 1330 Post Oak Boulevard, First Floor Auditorium, Houston, Texas, on Thursday, June 10, 2010, at 9:00 AM local time, in order to:

(1)

elect our directors for a term of one year;



(2)

approve a proposal to authorize us, with the approval of our Board of Directors, to sell shares of our common stock during the next twelve months at a price below our then current net asset value per share;



(3)

ratify our appointment of Grant Thornton LLP as our independent registered public accounting firm for the year ending December 31, 2010; and



(4)

transact such other business as may properly come before the meeting or any adjournment thereof.

        If you were a stockholder as of the close of business on April 1, 2010, you are entitled to vote at the meeting and at any adjournment thereof.

        Please indicate your vote as to the matters to be acted on at the meeting by following the instructions provided in the enclosed proxy card or voting instruction form, whether or not you plan on attending the meeting. If you plan to attend the meeting and wish to vote or change your vote there, please review the instructions set forth in the accompanying proxy statement under the caption "Voting Information."

        We have enclosed a copy of our Annual Report on Form 10-K for the year ended December 31, 2009, with this notice and proxy statement.

Dated:                             , 2010

Table of Contents

PROXY STATEMENT FOR 2010 ANNUAL MEETING OF STOCKHOLDERS

TABLE OF CONTENTS

Table of Contents

Main Street Capital Corporation
1300 Post Oak Boulevard, Suite 800
Houston, Texas 77056

PROXY STATEMENT
2010 ANNUAL MEETING OF STOCKHOLDERS

GENERAL
INFORMATION

        We are mailing this proxy statement and accompanying proxy card to our stockholders beginning on                                    , 2010. Our Board of Directors is soliciting your proxy to vote your shares at our 2010 Annual Meeting of Stockholders (the "Annual Meeting") to be held on June 10, 2010 at 1330 Post Oak Boulevard, First Floor Auditorium, Houston, Texas, at 9:00 AM local time. We will bear all expenses incurred in connection with this proxy solicitation, which we expect to conduct primarily by mail. We have engaged Laurel Hill Advisory Group LLC to assist in the solicitation for a fee that will not exceed $6,500, plus out-of-pocket expenses. In addition, our officers and regular employees may solicit your proxy by telephone, by facsimile transmission or in person, for which they will not be separately compensated. If your shares are held through a broker or other nominee (i.e., in "street name"), we have requested that your broker or nominee forward this proxy statement to you and obtain your voting instructions, for which we will reimburse them for reasonable out-of-pocket expenses.

VOTING INFORMATION

Record Date and Who May Vote

        Our Board of Directors selected April 1, 2010 as the record date (the "Record Date") for determining stockholders entitled to vote at the Annual Meeting. This means that if you were a registered stockholder with our transfer agent and registrar, American Stock Transfer and Trust Company, on the Record Date, you may vote your shares on the matters to be considered by our stockholders at the Annual Meeting. If your shares were held in street name on that date, the broker or other nominee that was the record holder of your shares has the authority to vote them at the Annual Meeting. They have forwarded to you this proxy statement seeking your instructions on how you want your shares voted.

        On the Record Date, 15,082,681 shares of our common stock were outstanding. Each outstanding share of common stock entitles its holder to one vote on each matter to be acted on at the Annual Meeting.

How to Vote

        For shares held of record, you can vote your shares in person at the Annual Meeting or vote now by giving us your proxy. You may give us your proxy by completing the enclosed proxy card and returning it in the enclosed U.S. postage-prepaid envelope, or by calling a toll-free telephone number or using the Internet as further described in the enclosed proxy card. In either case, telephone and Internet voting procedures have been designed to verify your identity through a personal identification or control number and to confirm that your voting instructions have been properly recorded. If you vote using either of these electronic means, you will save us return mail expense.

        By giving us your proxy, you will be directing us on how to vote your shares at the Annual Meeting. Even if you plan on attending the Annual Meeting, we urge you to vote now by giving us your proxy. This will ensure that your vote is represented at the Annual Meeting. If you do attend the Annual Meeting, you can change your vote at that time, if you then desire to do so.

Table of Contents

        If your shares are held in street name, the broker or nominee that holds your shares has the authority to vote them, absent your approval, only as to routine matters, which, in the case of the Annual Meeting, only applies to the proposal to ratify our appointment of our independent registered public accounting firm. For all other matters to be voted on at the Annual Meeting, the broker or nominee that holds your shares will need to obtain your authorization to vote those shares and has enclosed a voting instruction form with this proxy statement. In either case, they will vote your shares as you direct on their voting instruction form. You can vote by completing the enclosed voting instruction form and returning it in the enclosed U.S. postage-prepaid envelope. If you want to vote your shares in person at the Annual Meeting, you must obtain a valid proxy from your broker or nominee. You should refer to the instructions provided in the enclosed voting instruction form for further information. Additionally, the availability of telephone or Internet voting depends on the voting process used by the broker or nominee that holds your shares.

        You may receive more than one proxy statement and proxy card or voting instruction form if your shares are held through more than one account (e.g., through different brokers or nominees). Each proxy card or voting instruction form only covers those shares of common stock held in the applicable account. If you hold shares in more than one account, you will have to provide voting instructions as to all your accounts to vote all your shares.

How to Revoke or Change Your Vote

        For shares held of record, you may revoke a proxy or change your vote at any time before it is exercised by written notice to our Corporate Secretary, granting a new proxy or by voting in person at the Annual Meeting. Unless you attend the Annual Meeting and vote your shares in person, you should change your vote using the same method (by telephone, Internet or mail) that you first used to vote your shares. That way, the inspectors of election for the meeting will be able to verify your latest vote.

        For shares held in street name, you should follow the instructions in the voting instruction form provided by your broker or nominee to change your vote. If you want to change your vote as to shares held in street name by voting in person at the Annual Meeting, you must obtain a valid proxy from the broker or nominee that holds those shares for you.

Quorum

        The Annual Meeting will be held only if a quorum exists. The presence at the Annual Meeting, in person or by proxy, of holders of a majority of our outstanding shares of common stock as of the Record Date will constitute a quorum. If you attend the meeting or vote your shares using the enclosed proxy card or voting instruction form (including any telephone or Internet voting procedures provided), your shares will be counted toward a quorum, even if you abstain from voting on a particular matter. Shares held by brokers and other nominees as to which they have not received voting instructions from the beneficial owners and lack the discretionary authority to vote on a particular matter are called "broker non-votes" and will count for quorum purposes.

Proposals to Be Voted on; Vote Required; and How Votes Are Counted

        We are asking you to vote on the following:

•

the election of all of the members of our Board of Directors;



•

the proposal to authorize us, with approval of our Board of Directors, to sell shares of our common stock during the next twelve months at a price below our then current net asset value per share; and

2

Table of Contents

•

the ratification of our appointment of Grant Thornton LLP as our independent registered public accounting firm for the year ending December 31, 2010.

        Election of Directors.    The affirmative vote, in person or by proxy, of a plurality of all the votes cast at the Annual Meeting is sufficient to elect a director. Each share may be voted for each of the six director nominees. Votes that are withheld and broker non-votes will have no effect on the outcome of the vote on this item.

        Approval to Authorize the Sale of Common Stock, with Approval of our Board of Directors, During the Next Twelve Months at a Price Below Net Asset Value Per Share.    Under the Investment Company Act of 1940, or the 1940 Act, the affirmative vote of (1) the holders of a majority of the shares of stock outstanding and entitled to vote at the Annual Meeting; and (2) the holders of a majority of the shares of stock outstanding and entitled to vote at the Annual Meeting that are not held by affiliated persons of our company (as such term is defined in the 1940 Act) is required to approve this proposal. For purposes of this proposal, the 1940 Act defines "a majority of the outstanding shares" as: (A) 67% or more of the voting securities of a company present at a meeting if the holders of more than 50% of the outstanding voting securities of such company are present or represented by proxy; or (B) 50% of the outstanding voting securities of such company, whichever is less. Abstentions and broker non-votes will have the effect of votes against this proposal.

        Ratification of Independent Registered Public Accounting Firm.    The affirmative vote of a majority of the votes cast at the Annual Meeting, in person or by proxy, is required to ratify the appointment of Grant Thornton LLP to serve as our independent registered public accounting firm. Abstentions will not be included in determining the number of votes cast and, as a result, will not have any effect on the result of the vote.

        We are not aware of any other matters that may be presented or acted on at the Annual Meeting. If you vote by signing and returning the enclosed proxy card or using the telephone or Internet voting procedures, the individuals named as proxies on the card may vote your shares, in their discretion, on any other matter requiring a stockholder vote that comes before the Annual Meeting.

Confidential Voting

        All voted proxies and ballots will be handled to protect your voting privacy as a stockholder. Your vote will not be disclosed except:

•

to meet any legal requirements;



•

in limited circumstances such as a proxy contest in opposition to our Board of Directors;



•

to permit independent inspectors of election to tabulate and certify your vote; or



•

to adequately respond to your written comments on your proxy card.

ELECTION OF DIRECTORS

(ITEM 1)

        Pursuant to our articles of incorporation, each member of our Board of Directors serves a one-year term, until the next annual meeting of stockholders and until his respective successor is duly qualified and elected. Currently, our Board of Directors has six members.

        The term of office of all directors will expire at this year's Annual Meeting. On the nomination of our Board of Directors, Messrs. Michael Appling Jr., Joseph E. Canon, Arthur L. French, William D. Gutermuth, Vincent D. Foster and Todd A. Reppert will stand for reelection as directors at the Annual Meeting for a term of one year.

3

Table of Contents

        Unless otherwise directed, the persons named as proxies on the enclosed proxy card intend to vote "FOR" the election of the nominees. If any nominee should become unavailable for election, the shares will be voted for such substitute nominee as may be proposed by our Board of Directors. However, we are not aware of any circumstances that would prevent any of the nominees from serving.

        Set forth below is certain information (as of April 15, 2010) with respect to the nominees for election as directors. In addition to the information presented below regarding each nominee's specific experience, qualifications, attributes and skills that led our Board of Directors to the conclusion that he should serve as a director, we also believe that all of our director nominees have a reputation for integrity, honesty and adherence to high ethical standards. They each have demonstrated business acumen and an ability to exercise sound judgment, as well as a commitment of service to Main Street and our Board of Directors. Certain of our directors who are also our officers may serve as directors of, or on the boards of, certain of our portfolio companies. The business address of each nominee listed below is 1300 Post Oak Boulevard, Suite 800, Houston, Texas 77056.

Nominees

4

Table of Contents

5

Table of Contents

6

Table of Contents

        The affirmative vote, in person or by proxy, of a plurality of all the votes cast at the Annual Meeting is sufficient to elect a director. Each share may be voted for each of the six director nominees. Votes that are withheld and broker non-votes will have no effect on the outcome of the vote on this item.

THE BOARD OF DIRECTORS RECOMMENDS YOU VOTE "FOR" THE NOMINEES
NAMED IN THIS PROXY STATEMENT.

7

Table of Contents

CORPORATE GOVERNANCE

        We maintain a corporate governance section on our Web site which contains copies of the charters for the committees of our Board of Directors. The corporate governance section may be found at http://mainstcapital.com under "Governance" in the "Investor Relations" section of our Web site. The corporate governance section contains the following documents, which are available in print to any stockholder who requests a copy in writing to Main Street Capital Corporation, Corporate Secretary's Office, 1300 Post Oak Blvd., Suite 800, Houston, Texas 77056:

Audit Committee Charter
Nominating and Corporate Governance Committee Charter
Compensation Committee Charter

        In addition, our Code of Business Conduct and Ethics and our Corporate Governance and Stock Ownership Guidelines may be found at http://mainstcapital.com under "Governance" in the "Investor Relations" section of our Web site and is available in print to any stockholder who requests a copy in writing.

Director Independence

        Our Board of Directors consists of six members, four of whom are classified under applicable listing standards of the Nasdaq Stock Market as "independent" directors and under Section 2(a)(19) of the 1940 Act as not "interested persons." Based on these independence standards, our Board of Directors has affirmatively determined that the following directors are independent:

Michael Appling Jr.
Joseph E. Canon
Arthur L. French
William D. Gutermuth

        Our Board of Directors considered the following relationships in evaluating our directors' independence under the applicable listing standards of the Nasdaq Stock Market. Both Messrs. Canon and French had previously been limited partners in Main Street Mezzanine Fund, LP, and Mr. French had previously served on the Advisory Board of Main Street Capital Partners, LLC, one of our wholly owned subsidiaries and the investment advisor to Main Street Mezzanine Fund, LP and Main Street Capital II, LP, prior to our acquisition of these entities. Messrs. Canon and French are also limited partners in Main Street Capital II, LP, a Small Business Investment Company, or SBIC, fund licensed by the United States Small Business Administration, in which we acquired a majority limited partnership interest in January 2010. The Company did not acquire any limited partnership interests from Messrs. Canon and French in the transaction. Our Board of Directors determined that those prior relationships would not impact the ability of either Mr. Canon or Mr. French to exercise independent judgment and do not impair the independence of either of them.

Communications with the Board

        Stockholders or other interested persons may send written communications to the members of our Board of Directors, addressed to Board of Directors, c/o Main Street Capital Corporation, Corporate Secretary's Office, 1300 Post Oak Blvd., Suite 800, Houston, Texas 77056. All communications received in this manner will be delivered to one or more members of our Board of Directors.

Board Leadership Structure

        Mr. Foster currently serves as both our Chief Executive Officer and as the Chairman of our Board of Directors. As our Chief Executive Officer, Mr. Foster is an "interested person" under Section 2(a)(19) of the 1940 Act. The Board believes that the Company's Chief Executive Officer is

8

Table of Contents

currently best situated to serve as Chairman because he is the director most familiar with the Company's business and industry, and most capable of effectively identifying strategic priorities and leading the discussion and execution of strategy. Independent directors and management have different perspectives and roles in strategy development. The Company's independent directors bring experience, oversight and expertise from outside the company and industry, while the Chief Executive Officer brings company-specific and industry-specific experience and expertise. The Board believes that the combined role of Chairman and Chief Executive Officer promotes strategy development and execution, and facilitates information flow between management and the Board, which are essential to effective governance.

        One of the key responsibilities of the Board is to develop strategic direction and hold management accountable for the execution of strategy once it is developed. The Board believes the combined role of Chairman and Chief Executive Officer, together with an independent Lead Director as described below, is in the best interest of our stockholders because it provides the appropriate balance between strategy development and independent oversight of management.

        Our Board of Directors designated Arthur L. French as Lead Director to preside at all executive sessions of non-management directors. In the Lead Director's absence, the remaining non-management directors may appoint a presiding director by majority vote. The non-management directors meet in executive session without management on a regular basis. The Lead Director also has the responsibility of consulting with management on Board and committee meeting agendas, acting as a liaison between management and the non-management directors, including maintaining frequent contact with the Chairman and Chief Executive Officer and facilitating collaboration and communication between the non-management directors and management. Stockholders or other interested persons may send written communications to Arthur L. French, addressed to Lead Director, c/o Main Street Capital Corporation, Corporate Secretary's Office, 1300 Post Oak Blvd., Suite 800, Houston, Texas 77056.

Board of Directors and its Committees

        Board of Directors.    Our Board of Directors met nine times and acted by unanimous written consent six times during 2009. All directors attended 100% of the meetings of the Board of Directors and of the committees on which they served during 2009. Our Board of Directors expects each director to make a diligent effort to attend all Board and committee meetings, as well as each Annual Meeting of Stockholders.

        Committees.    Our Board of Directors currently has, and appoints the members of, standing Audit, Compensation and Nominating and Corporate Governance Committees. Each of those committees is comprised entirely of independent directors and has a written charter approved by our Board of Directors. The current members of the committees are identified in the following table.

        Audit Committee.    During the year ended December 31, 2009, the Audit Committee met five times. The Audit Committee is responsible for selecting, engaging and discharging our independent accountants, reviewing the plans, scope and results of the audit engagement with our independent accountants, approving professional services provided by our independent accountants (as well as the

9

Table of Contents

compensation for those services), reviewing the independence of our independent accountants and reviewing the adequacy of our internal control over financial reporting. In addition, the Audit Committee is responsible for assisting our Board of Directors, in connection with its review and approval of the determination of the fair value of our debt and equity investments, and other financial investments, that are not publicly traded or for which current market values are not readily available. Our Board of Directors has determined that Mr. Appling is an "Audit Committee financial expert" as defined by the Securities and Exchange Commission, or SEC, and an independent director. Messrs. Canon and French are the other members of the Audit Committee. For more information on the backgrounds of these directors, see their biographical information under "Election of Directors" above.

        Compensation Committee.    During the year ended December 31, 2009, the Compensation Committee met five times and acted by unanimous written consent once. The Compensation Committee determines the compensation and related benefits for our executive officers including the amount of salary, bonus and stock-based compensation to be included in the compensation package for each of our executive officers. The actions of the Compensation Committee are generally reviewed and ratified by the entire Board of Directors, excluding the employee directors. The members of the Compensation Committee are Messrs. Canon, French and Gutermuth.

        Nominating and Corporate Governance Committee.    During the year ended December 31, 2009, the Nominating and Corporate Governance Committee met five times. The Nominating and Corporate Governance Committee is responsible for determining criteria for service on our Board of Directors, identifying, researching and recommending to the Board of Directors director nominees for election by our stockholders, selecting nominees to fill vacancies on our Board of Directors or a committee of the Board, developing and recommending to our Board of Directors any amendments to our corporate governance principles and overseeing the self-evaluation of our Board of Directors and its committees and evaluations of our management. The members of the Nominating and Corporate Governance Committee are Messrs. Appling, Canon and Gutermuth.

Compensation Committee Interlocks and Insider Participation

        Each member of the Compensation Committee is independent for purposes of the applicable listing standards of the Nasdaq Stock Market. No member of the Compensation Committee (1) was, during the year ended December 31, 2009, or had previously been, an officer or employee of Main Street or any of its subsidiaries or (2) had any material interest in a transaction of Main Street or any of its subsidiaries or a business relationship with, or any indebtedness to, Main Street or any of its subsidiaries. No interlocking relationship existed during the year ended December 31, 2009 between any member of the Board of Directors or the Compensation Committee and an executive officer of Main Street.

Director Nomination Process

        Our Nominating and Corporate Governance Committee has determined that a candidate for election to our Board of Directors must satisfy certain general criteria, including, among other things:

•

be an individual of the highest character and integrity and have an inquiring mind, vision, a willingness to ask hard questions and the ability to work professionally with others;



•

be free of any conflict of interest that would violate any applicable law or regulation or interfere with the proper performance of the responsibilities of a director;



•

be willing and able to devote sufficient time to the affairs of our company and be diligent in fulfilling the responsibilities of a member of our Board of Directors and a member of any committee thereof (including: developing and maintaining sufficient knowledge of our company

10

Table of Contents

and the specialty finance industry in general; reviewing and analyzing reports and other information important to responsibilities of the Board of Directors and any committee of our Board of Directors; preparing for, attending and participating in meetings of our Board of Directors and meetings of any committee of our Board of Directors; and satisfying appropriate orientation and continuing education guidelines); and

•

have the capacity and desire to represent the balanced, best interests of our stockholders as a whole and not primarily a special interest group or constituency.

        The Nominating and Corporate Governance Committee seeks to identify potential director candidates who will strengthen the Board of Directors and will contribute to the overall mix of general criteria identified above. In addition to the general criteria, the Nominating and Corporate Governance Committee considers specific criteria, such as particular skills, experiences (whether in business or in other areas such as public service, academia or scientific communities), areas of expertise, specific backgrounds, and other characteristics, that should be represented on the Board of Directors to enhance its effectiveness and the effectiveness of its committees. The Nominating and Corporate Governance Committee does not have a formal policy with respect to diversity; however, the Board and the Nominating Committee believe that it is essential that the Board members represent diverse viewpoints and a diverse mix of the specific criteria above. The process of identifying potential director candidates includes establishing procedures for soliciting and reviewing potential nominees from directors and for advising those who suggest nominees of the outcome of such review. The Nominating and Corporate Governance Committee also has the authority to retain and terminate any search firm used to identify director candidates.

        Any stockholder may nominate one or more persons for election as one of our directors at an annual meeting of stockholders if the stockholder complies with the notice, information and consent provisions contained in our by-laws and any other applicable law, rule or regulation regarding director nominations. When submitting a nomination to our company for consideration, a stockholder must provide certain information that would be required under applicable SEC rules, including the following minimum information for each director nominee: full name, age and address; class, series and number of any shares of our stock beneficially owned by the nominee, if any; the date such shares were acquired and the investment intent of such acquisition; whether such stockholder believes the nominee is an "interested person" of our company, as defined in 1940 Act; and all other information required to be disclosed in solicitations of proxies for election of directors in an election contest or is otherwise required, including the nominee's written consent to being named in the proxy statement as a nominee and to serving as a director if elected. See "Stockholders' Proposals" in this proxy statement and our by-laws for other requirements of stockholder proposals.

        The Nominating and Corporate Governance Committee will consider candidates identified through the processes described above, and will evaluate each of them, including incumbents, based on the same criteria. The Nominating and Corporate Governance Committee also takes into account the contributions of incumbent directors as Board members and the benefits to us arising from their experience on our Board of Directors. Although the Nominating and Corporate Governance Committee will consider candidates identified by stockholders, the Nominating and Corporate Governance Committee may determine not to recommend those candidates to our Board of Directors, and our Board of Directors may determine not to nominate any candidates recommended by the Nominating and Corporate Governance Committee. None of the director nominees named in this proxy statement were nominated by stockholders.

11

Table of Contents

Board's Role in the Oversight of Risk Management

        Our Board of Directors as a whole has responsibility for risk oversight, with reviews of certain areas being conducted by the relevant Board Committees that report on their deliberations to the full Board. The oversight responsibility of the Board and its Committees is enabled by management reporting processes that are designed to provide visibility to the Board about the identification, assessment and management of critical risks and management's risk mitigation strategies. Areas of focus include competitive, economic, operational, financial (accounting, credit, liquidity and tax), legal, regulatory, compliance and other risks. The Board and its Committees oversee risks associated with their respective principal areas of focus, as summarized below. Committees meet in executive session with key management personnel regularly and with representatives of outside advisors as necessary.

12

Table of Contents

COMPENSATION OF DIRECTORS

        The following table sets forth the compensation that we paid during the year ended December 31, 2009 to our directors. Directors who are also employees of Main Street or any of its subsidiaries do not receive compensation for their services as directors.

Director Compensation Table

        The compensation for non-employee directors for 2009 was comprised of cash compensation paid to or earned by directors in connection with their service as a director. That cash compensation consisted of an annual retainer of $30,000, and an additional $20,000 retainer for the Lead Director. Non-employee directors will not receive fees based on meetings attended absent circumstances that require an exceptionally high number of meetings within an annual period. We also reimburse our non-employee directors for all reasonable expenses incurred in connection with their service on our Board. The chairs of our Board committees receive additional annual retainers as follows:

•

the chair of the Audit Committee: $10,000; and



•

the chair of each of the Compensation and Nominating and Corporate Governance committees: $5,000.

        Our 2008 Non-Employee Director Restricted Stock Plan provides a means through which we may attract and retain qualified non-employee directors to enter into and remain in service on our Board of Directors. Under our 2008 Non-Employee Director Restricted Stock Plan, at the beginning of each one-year term of service on our Board of Directors, each non-employee director will receive a number of shares equivalent to $30,000 worth of shares based on the closing price of a share of our common stock on the Nasdaq Global Select Market (or other exchange on which are shares are then listed) on the date of grant. Forfeiture provisions will lapse as to an entire award at the end of the one-year term.

13

Table of Contents

EXECUTIVE OFFICERS

        Our executive officers serve at the discretion of our Board of Directors. The following persons serve as our executive officers in the following capacities (information as of April 15, 2010):

        For more information on Mr. Foster, Chairman of the Board and Chief Executive Officer, and Mr. Reppert, Director, President and Chief Financial Officer, see their biographical information under "Election of Directors" above.

        Rodger A. Stout serves as our Chief Compliance Officer, Senior Vice President—Finance and Administration and Treasurer. Mr. Stout has been the chief financial officer of Main Street Mezzanine Management, LLC, Main Street Capital Partners, LLC and the general partner of Main Street Capital II, LP since 2006. From 2000 to 2006, Mr. Stout was senior vice president and chief financial officer for FabTech Industries, Inc., one of the largest domestic structural steel fabricating companies. From 1985 to 2000, he was a senior financial executive for Jerold B. Katz Interests. He held numerous positions over his 15-year tenure with this national scope financial services conglomerate. Those positions included director, executive vice president, senior financial officer and investment officer. Prior to 1985, Mr. Stout was an international tax executive in the oil and gas service industry.

        Curtis L. Hartman serves as one of our Senior Vice Presidents and is currently a member of our Investment Committee. Mr. Hartman has been a managing director of Main Street Mezzanine Management, LLC and Main Street Capital Partners, LLC since 2002 and a managing director of the general partner for Main Street Capital II, LP since January 2006. From 2000 to 2002, he was a director of the predecessor entity of Main Street Mezzanine Fund. From 1999 to 2000, Mr. Hartman was an investment adviser for Sterling City Capital, LLC. Concurrently with joining Sterling City Capital, he joined United Glass Corporation, a Sterling City Capital portfolio company, as director of corporate development. Prior to joining Sterling City Capital, Mr. Hartman was a manager with PricewaterhouseCoopers LLP, in its M&A/Transaction Services group. Prior to that, he was employed as a senior auditor by Deloitte & Touche LLP.

        Dwayne L. Hyzak serves as one of our Senior Vice Presidents. Mr. Hyzak has been a managing director of Main Street Mezzanine Management LLC and Main Street Capital Partners, LLC since 2002. He has also been a managing director of the general partner for Main Street Capital II, LP since January 2006. From 2000 to 2002, Mr. Hyzak was a director of integration with Quanta Services, Inc. (NYSE: PWR), an electrical and telecommunications contracting company, where he was principally focused on the company's mergers and acquisitions and corporate finance activities. Prior to joining Quanta Services, Inc., he was a manager with Arthur Andersen LLP in its Transaction Advisory Services group.

        David L. Magdol serves as one of our Senior Vice Presidents. Mr. Magdol has been a managing director of Main Street Mezzanine Management, LLC and Main Street Capital Partners, LLC since

14

Table of Contents

2002 and a managing director of the general partner for Main Street Capital II, LP since January 2006. From 2000 to 2002, Mr. Magdol was a vice president in the Investment Banking Group of Lazard Freres & Co. LLC. From 1996 to 2000, Mr. Magdol served as a vice president of McMullen Group, a private equity investment firm capitalized by Dr. John J. McMullen. From 1993 to 1996, Mr. Magdol worked in the Structured Finance Services Group of Chemical Bank as a management associate.

        Jason B. Beauvais serves as our Vice President, General Counsel and Secretary. Prior to joining us in June 2008, Mr. Beauvais was an attorney with Occidental Petroleum Corporation, an international oil and gas exploration and production company, since August 2006. From October 2002 to August 2006, he was an associate at Baker Botts L.L.P., where he primarily counseled companies in public issuances and private placements of debt and equity and handled a wide range of general corporate and securities matters as well as mergers and acquisitions.

        Michael S. Galvan serves as our Vice President and Chief Accounting Officer. Prior to joining us in February 2008, Mr. Galvan was senior manager of financial operations with Direct Energy, a retail gas and electricity service provider since October 2006. From September 2005 to October 2006, he was a senior audit manager with Malone & Bailey, PC, where he managed and coordinated audits of both publicly traded and private companies. From March 2003 to September 2005, Mr. Galvan was Director of Bankruptcy Coordination at Enron Corporation. Prior to March 2003, he served in other executive positions at various Enron affiliates.

COMPENSATION DISCUSSION AND ANALYSIS

        The following Compensation Discussion and Analysis, or CD&A, provides information relating to the 2009 compensation of Main Street's Chief Executive Officer, President and Chief Financial Officer and four other most highly compensated executive officers during 2009. Those six individuals are referred to in this CD&A as the Named Executive Officers, or NEOs.

Compensation Philosophy and Objectives

        The Main Street compensation system was developed by the Compensation Committee and approved by all independent directors. The system is designed to attract and retain key executives, motivate them to achieve the company's short-term and long-term objectives, reward them for superior performance and align their interests with those of the company's stockholders. Significant elements of the compensation arrangements with the NEOs (other than the Chief Executive Officer) in 2009 were set forth in separate employment agreements Main Street had entered into with them in connection with the company's initial public offering. As more fully described below in "Employment Agreements," pursuant to amendments entered into in 2009, each of these employment agreements terminated as of December 31, 2009. While all of the NEOs remained in their current positions, we have elected not to renew or enter into new employment agreements with them at this time. Main Street's Chief Executive Officer has entered into a confidentiality and non-compete agreement with us and serves at the discretion of the Board of Directors. The structure of Main Street's incentive compensation programs is designed to encourage and reward the following, among other things:

•

achievement of income and capital gains to sustain and grow the company's dividend payments;



•

maintenance of liquidity and capital flexibility to accomplish the company's business objectives, including the preservation of investor capital;



•

superior risk-adjusted returns on the company's investment portfolio; and



•

management team development.

        The Compensation Committee has the primary authority to establish compensation for the NEOs and other key employees and administers all executive compensation arrangements and policies. Main

15

Table of Contents

Street's Chief Executive Officer assists the Compensation Committee by providing annual recommendations regarding the compensation of NEOs and other key employees, excluding himself. The Committee exercises its discretion by modifying or accepting these recommendations. The Chief Executive Officer routinely attends a portion of the Compensation Committee meetings. However, the Committee also meets in executive session without the Chief Executive Officer or other members of management present when discussing the Chief Executive Officer's compensation and other occasions as determined by the Committee.

        The Compensation Committee takes into account competitive market practices with respect to the salaries and total direct compensation of the NEOs. Members of the Committee consider market practices by reviewing proxy statements or similar information made available by other internally managed business development companies, or BDCs, under the 1940 Act. The Committee also has the authority to utilize compensation consultants to better understand competitive pay practices. In this regard, the Committee engaged a compensation consultant in late 2008 to study the level and structure of compensation paid to our NEOs as compared to other internally managed business development companies, private equity firms and specialty finance companies (both public and private). The Committee considered the findings of the compensation consultant but did not make any material changes to the compensation program in 2009 for our NEOs based on their findings. The Committee engaged the compensation consultant again in early 2010 to provide the committee an updated analysis of compensation paid to the executive officers of other internally managed business development companies. The Committee expects to use this analysis, among other things, in evaluating the future compensation of our NEOs.

Assessment of Market Data

        To assess the competitiveness of executive compensation levels, the Compensation Committee analyzes a comparative group of BDCs and reviews their competitive performance and compensation levels. This analysis centers around key elements of compensation practices within the BDC industry in general and, more specifically, compensation practices at internally managed BDCs reasonably comparable in asset size, typical investment size and type, market capitalization and general business scope to the company. Since there are relatively few internally managed BDCs, and because of Main Street's relative asset size and market capitalization in comparison to many BDCs, the Compensation Committee includes certain internally managed BDCs in Main Street's peer group that are substantially larger than the company. The peer group consists of the following companies: Hercules Technology Growth Capital, Inc., MCG Capital Corporation, Capital Southwest Corporation, Medallion Financial Corp. and Triangle Capital Corporation. In addition to analyzing other BDCs, the Committee also evaluated the compensation structure of the private equity industry through third party compensation surveys.

        Items reviewed include, but are not necessarily limited to, base compensation, bonus compensation, equity option awards, restricted stock awards, and other compensation as detailed in the respective proxies, research analysts' reports and other publicly available information. In addition to actual levels of compensation, the Compensation Committee also analyzes the approach other BDCs are taking with regard to their compensation practices. Such items include, but are not necessarily limited to, the use of employment agreements for certain employees, a mix of cash and equity compensation, the use of third party compensation consultants and certain corporate and executive performance measures established to achieve long-term total return for stockholders. Although each of the peer companies is not precisely comparable in size, scope and operations to the company, the Committee believes that they are the most relevant comparable companies available with disclosed executive compensation data, and provide a good representation of competitive compensation levels for the company's executives.

16

Table of Contents

Assessment of Company Performance

        The Compensation Committee believes that consistent financial performance coupled with reasonable, long-term stockholders' returns and proportional employee compensation are essential components for Main Street's long-term business success. Main Street typically makes three to seven year investments in lower middle-market companies. The company's business plan involves taking on investment risk over an extended period of time, and a premium is placed on the ability to maintain stability of net asset values and continuity of earnings to pass through to stockholders in the form of recurring dividends. Main Street's strategy is to generate current income from debt investments and to realize capital gains from equity-related investments. This income supports the payment of dividends to stockholders. The recurring payment of dividends requires a methodical investment acquisition approach and active monitoring and management of the investment portfolio over time. A meaningful part of the company's employee base is dedicated to the maintenance of asset values and expansion of this recurring income to sustain and grow dividends. The Committee believes that stability with regard to the management team is important in achieving successful implementation of the company's strategy.

Executive Compensation Components

        For 2009, the components of Main Street's direct compensation program for NEOs include:

•

base salary;



•

annual cash bonuses;



•

long-term compensation pursuant to the 2008 Equity Incentive Plan; and



•

other benefits.

        The Compensation Committee designs each NEO's direct compensation package to appropriately reward the NEO for his contribution to the company. The judgment and experience of the Compensation Committee are weighed with performance metrics and consultation with the Chief Executive Officer to determine the appropriate mix of compensation for each individual. Cash compensation consisting of base salary and discretionary bonuses tied to achievement of individual performance goals reviewed and approved by the Compensation Committee, as well as corporate objectives, is intended to motivate NEOs to remain with the company and work to achieve its business objectives. Stock-based compensation is awarded based on performance expectations reviewed and approved by the Committee for each NEO. The blend of short-term and long-term compensation may be adjusted from time to time to balance the Committee's views regarding the benefits of current cash compensation and appropriate retention incentives.

Base Salary

        Base salary is used to recognize the experience, skills, knowledge and responsibilities required of the NEOs in their roles. In connection with establishing the base salary of each NEO, the Compensation Committee and management considered a number of factors, including the seniority and experience level of the individual, the functional role of his position, the level of the individual's responsibility, the company's ability to replace the individual, the past base salary of the individual and the number of well-qualified candidates available in the area. In addition, the Committee considered publicly available information regarding the base salaries paid to similarly situated executive officers and other competitive market practices.

        The salaries of the NEOs are reviewed on an annual basis, as well as at the time of promotion or any substantial change in responsibilities. Each of the NEO employment agreements established a target for annual increase in base salary at 5%, but provided that any increase is at the sole discretion of the Committee. Each such employment agreement also provided that the base salary was not subject

17

Table of Contents

to reduction. The key factors in determining increases in salary level are relative performance and competitive pressures.

Annual Cash Bonuses

        Annual cash bonuses are intended to reward individual performance during the year and can therefore be highly variable from year to year. Bonus opportunities for the NEOs are determined by the Compensation Committee on a discretionary basis and are based on performance criteria, including corporate and individual performance goals and measures, set by the Committee with the Chief Executive Officer's input. As more fully described below in "Employment Agreements," the employment agreements of the NEOs provided for target annual cash bonus amounts as a percentage of base salary.

Long-Term Incentive Awards

        Main Street's Board and stockholders have approved the 2008 Equity Incentive Plan to provide stock-based awards as long-term incentive compensation to employees, including the NEOs. The company uses stock-based awards to (i) attract and retain key employees, (ii) motivate employees by means of performance-related incentives to achieve long-range performance goals, (iii) enable employees to participate in the company's long-term growth and (iv) link employees' compensation to the long-term interests of stockholders. At the time of each award, the Compensation Committee will determine the terms of the award, including any performance period (or periods) and any performance objectives relating to vesting of the award.

        Options.    The Compensation Committee may grant equity options to purchase Main Street's common stock (including incentive stock options and nonqualified stock options). The Committee expects that any options granted by it will represent a fixed number of shares of common stock, will have an exercise price equal to the fair market value of common stock on the date of grant, and will be exercisable, or "vested," at some later time after grant. Some stock options may provide for vesting simply by the grantee remaining employed by Main Street for a period of time, and some may provide for vesting based on the grantee and/or the company attaining specified performance levels. To date, the Committee has not granted any stock options to any NEO.

        Restricted Stock.    Main Street has received exemptive relief from the SEC that permits the company to grant restricted stock in exchange for or in recognition of services by its executive officers and employees. Pursuant to the 2008 Equity Incentive Plan, the Compensation Committee may award shares of restricted stock to plan participants in such amounts and on such terms as the Committee determines in its sole discretion, provided that such awards are consistent with the conditions set forth in the SEC's exemptive order. Each restricted stock grant will be for a fixed number of shares as set forth in an award agreement between the grantee and Main Street. Award agreements will set forth time and/or performance vesting schedules and other appropriate terms and/or restrictions with respect to awards, including rights to dividends and voting rights. As more fully described below, each of the NEO employment agreements provided for a target annual restricted stock award or an equitable substitute.

Other Benefits

        Main Street's NEOs participate in the same benefit plans and programs as the company's other employees, including comprehensive medical insurance, comprehensive dental insurance, business travel accident insurance, short term disability coverage, long term disability insurance, and vision care.

        Main Street maintains a 401(k) plan for all full-time employees who are at least 21 years of age through which the company makes non-discretionary matching contributions to each participant's plan account on the participant's behalf. For each participating employee, the company's contribution is

18

Table of Contents

generally a match of the employee's contributions up to a 4.5% contribution level with a maximum annual regular matching contribution of $11,025 during 2009. All contributions to the plan, including those made by the Company, vest immediately. The Board of Directors may also, at its sole discretion, make additional contributions to employee 401(k) plan accounts, which would vest on the same basis as other employer contributions.

Perquisites

        The company provides no other material benefits, perquisites or retirement benefits to the NEOs.

Employment Agreements

        In connection with Main Street's initial public offering, the company entered into employment agreements with each of its NEOs, other than Mr. Foster, its Chief Executive Officer. Initial terms of the employment agreements extended to December 31, 2010. However, in 2009, the employment agreements were amended to (i) shorten their terms to expire on December 31, 2009, (ii) conform certain dates with respect to cash bonuses and equity awards due to the reduced terms of the agreements and (iii) provide that the number of shares to be issued pursuant to any dollar-based equity awards will be determined based upon the greater of the market price of our common stock at the time of issuance and our last reported net asset value per share. Although the employment agreements have expired and the Company does not intend to renew or enter into new employment agreements at this time, all of the NEOs have remained in their current positions and are subject to the post-employment confidentiality and non-solicitation provisions in their Restricted Stock Grant Agreements. As the Chairman of the Board of Directors and Chief Executive Officer, Mr. Foster does not have an employment agreement and serves as an executive officer at the direction and discretion of the Board of Directors. However, Mr. Foster has executed a confidentiality and non-compete agreement with the company. The NEO employment agreements specified an initial base salary that was paid in 2007 and contemplated a 5% target annual increase in base salary (provided that any increase was in the sole discretion of the Compensation Committee).

        Each NEO employment agreement, as amended, specified a target discretionary annual bonus as a percentage of his then current base salary based upon achieving the performance objectives established by the Compensation Committee. Under the NEO employment agreements, the applicable NEOs had referenced target bonus amounts for each of the years ending December 31, 2008 and 2009. The target bonus amounts for Mr. Reppert were 50% and 60% of his base salary, respectively, for each of those calendar years. The target bonus amounts for Messrs. Stout, Hartman, Hyzak and Magdol were 40% and 50% of their base salaries for each of those calendar years, respectively. The Compensation Committee had established applicable individual and corporate performance objectives, but retained discretion to determine the actual bonus awarded to each NEO annually.

        Each NEO employment agreement, as amended, also provided for the initial grant of restricted stock in an amount equal to 40,000 shares for Mr. Reppert and 30,000 shares for each of Messrs. Stout, Hartman, Hyzak and Magdol in respect of such executive's service performed in 2007, including in connection with the successful completion of the company's initial public offering, and further service performed in 2008. In addition, the NEO employment agreements, as amended, provided for targeted annual restricted stock awards for calendar year 2009 with a grant date valuation of 75% of base salary for Mr. Reppert and a grant date valuation of 50% of base salaries for each of Messrs. Stout, Hartman, Hyzak and Magdol, in each case subject to the Committee's discretion based on the satisfaction of objective, reasonable and attainable performance criteria established by the Committee. Restricted stock awards generally vest in equal annual portions over the four years subsequent to the date of grant. As discussed below, NEOs were granted certain amounts of restricted stock on July 1, 2009 that were not contemplated by their employment agreements primarily as an inducement for their entering into amendments to the employment agreement to, among other things, shorten the terms of such agreements.

19

Table of Contents

        The NEO employment agreements also provided for certain severance benefits to be paid by us to the NEOs who were parties to the NEO employment agreements upon termination of their employment after a change of control of the company. However, because all of the NEO employment agreements terminated on December 31, 2009 and no change of control of the company occurred prior to such date, no payouts will be made by us in connection with any of these arrangements.

Potential Payments Upon Change in Control

        Upon a change in control, equity-based awards issued under the 2008 Equity Incentive Plan will vest and/or become immediately exercisable or salable. In addition, upon termination of employment following a change in control, the NEOs who were parties to the NEO employment agreements would have been entitled to certain severance payments. However, as noted above, these employment agreements lapsed on December 31, 2009 without any change in control of the company occurring and, as a result, no payouts will be made by us in connection with any of these arrangements.

        2008 Equity Incentive Plan.    Upon specified transactions involving a change in control (as defined in the 2008 Equity Incentive Plan), all outstanding awards under the 2008 Equity Incentive Plan may either be assumed or substituted for by the surviving entity. If the surviving entity does not assume or substitute similar awards, the awards held by the plan participants will be subject to accelerated vesting in full and, in the case of options, then terminated to the extent not exercised within a designated time period.

        Transactions involving a "change in control" under the 2008 Equity Incentive Plan include:

•

a consolidation, merger, stock sale or similar transaction or series of related transactions in which Main Street is not the surviving corporation or which results in the acquisition of all or substantially all of the company's then outstanding common stock by a single person or entity or by a group of persons and/or entities acting in concert;



•

a sale or transfer of all or substantially all of the company's assets;



•

Main Street's dissolution or liquidation; or



•

a change in the membership of the company's Board of Directors such that the individuals who, as of the effective date of the plan, constitute the Board of Directors, whom are referred to as the Continuing Directors, and any new director whose election or nomination by the Board of Directors was approved by a vote of at least a majority of the Continuing Directors, cease to constitute at least a majority of the Board.

        The number of shares and value of restricted stock for the NEOs as of December 31, 2009 that would have vested under the acceleration scenarios described above is shown under the caption entitled "Compensation of Executive Officers—Outstanding Equity Awards at Fiscal Year-End."

Tax Deductibility of Compensation

        Section 162(m) of the Internal Revenue Code generally disallows a deduction to public companies to the extent of excess annual compensation over $1 million paid to certain executive officers, except for qualified performance-based compensation. Main Street's general policy, where consistent with business objectives, is to preserve the deductibility of executive officer compensation. The Compensation Committee may authorize forms of compensation that might not be deductible if the Committee deems such to be in the best interests of Main Street and its stockholders. The company had no nondeductible compensation paid to executive officers in 2009.

20

Table of Contents

Participation of Executives in Outside Public Directorships

        Our Board of Directors believes that there may be benefits to the company from our executive officers, including our NEOs, being involved in outside public company directorships. The business experience, knowledge and contacts gained by our executives in such capacities can be a valuable asset to the company. However, involvement in such outside public directorships can be time consuming and may take time away from the executives' responsibilities to the company. With this in mind, our Board of Directors implemented a policy starting in 2009 to permit executive officers to participate in outside public directorships with the prior approval of the independent members of our Board of Directors. The policy requires that 75% of the cash retainers for any such directorships be paid to the company. In 2009 this policy applied only to Mr. Foster since he was the only executive officer with any outside public directorships.

2009 Compensation Determination

        The Compensation Committee analyzed the competitiveness of the components of compensation described above on both an individual and aggregate basis. The Compensation Committee believes that the total compensation paid to the NEOs for the fiscal year ended December 31, 2009 achieves the overall objectives of Main Street's executive compensation program.

Determination of Annual Base Salary

        The Compensation Committee annually reviews the base salary of each executive officer, including each NEO, and determines whether or not to increase it in its sole discretion. Increases to base salary can be awarded to recognize, among other things, relative performance, relative cost of living and competitive pressures. Due to the difficult economic environment prevailing throughout the United States during 2008 and early 2009, Messrs. Foster and Reppert were paid 2009 annual base salaries equal to their 2008 annual base salaries, and Messrs. Stout, Hartman, Hyzak and Magdol were each paid 2009 annual base salaries of $223,229, a 3.8% increase from their 2008 annual base salaries.

Determination of Annual Cash Incentive Bonus

        Cash bonuses are determined annually by the Compensation Committee on a discretionary basis. The 2009 target cash bonus percentage of base salary for each NEO based on his employment agreement is presented below. The Committee, in its sole discretion, may award cash bonuses that exceed cash bonus targets if it believes that the performance of the NEO during the given year merits such a bonus.

        The Committee considered performance achievements in the determination of cash bonuses for 2009, including company performance and the personal performance of each individual. The performance goals used for determining the cash bonuses for NEOs included, among other things, the following:

•

Maintaining appropriate dividend payouts to stockholders;

21

Table of Contents

•

Maintaining liquidity and capital flexibility to accomplish the company's business objectives, including the preservation of investor capital;



•

Maintaining reasonable relative overall portfolio performance; and



•

Maintaining the highest ethical standards, internal controls and adherence to regulatory requirements.

        Although the performance of the Company and our NEOs individually in 2009 was consistent with expectations and compared favorably to Main Street's peer company group and industry indexes, management recommended and the Compensation Committee determined that, in light of the prevailing economic conditions which impact the business environment for virtually all companies, including the Company and our portfolio companies, no cash bonuses would be paid to NEOs for 2009. Instead, the Committee will consider awarding additional restricted stock in 2010 in lieu thereof. The absence of cash bonuses for 2009 does not reflect negatively on any individual executive's performance, but, instead, reflects the Compensation Committee's recognition of significant challenges in the economy during 2009 as well as the desire to restrain operating costs in the current economic environment.

Determination of Long-Term Incentive Awards

        Although grants of restricted stock were not contemplated by the employment agreements of Messrs. Reppert, Stout, Hartman, Hyzak and Magdol, the Compensation Committee granted those NEOs restricted stock under the 2008 Equity Incentive Plan on July 1, 2009 primarily as an inducement for their entering into the employment agreement amendments discussed above. Mr. Foster, who was not party to an employment agreement, was also granted restricted stock under the 2008 Equity Incentive Plan on July 1, 2009 based on his performance in 2008 and also to compensate him for forgoing a cash bonus award for 2008 in light of the economic environment in 2008 and 2009. The grant amount of restricted shares for each NEO in 2009 is presented under the caption entitled "Compensation of Executive Officers—Grants of Plan-Based Awards." All restricted stock grants to NEOs under the 2008 Equity Incentive Plan vest ratably over four years from the grant date.

COMPENSATION COMMITTEE REPORT

        We have reviewed and discussed the Compensation Discussion and Analysis included in this proxy statement with Main Street's management and, based on our review and discussions, we recommended to the Board of Directors of Main Street that the Compensation Discussion and Analysis be included in this proxy statement.

22

Table of Contents

COMPENSATION OF EXECUTIVE OFFICERS

        The following table summarizes compensation of our Chief Executive Officer, our President and Chief Financial Officer and our four highest paid executive officers who did not serve as our Chief Executive Officer or Chief Financial Officer during 2009, all of whom we refer to as our NEOs, for the fiscal year ended December 31, 2009.

Summary Compensation Table

23

Table of Contents

Grants of Plan-Based Awards

        The following table sets forth information regarding restricted stock awards granted to our NEOs in fiscal 2009:

24

Table of Contents

Outstanding Equity Awards at Fiscal Year-End

        The following table sets forth the awards of restricted stock for which forfeiture provisions have not lapsed and remain outstanding at December 31, 2009:

Equity Awards Vested in 2009 Fiscal Year

        The following table sets forth information regarding shares of restricted stock for which forfeiture restrictions lapsed during the fiscal year ended December 31, 2009:

Risk Management and Compensation Policies and Practices

        We believe that risks arising from our compensation policies and practices for our employees are not reasonably likely to have a material adverse effect on the company. In addition, the Compensation Committee believes that the mix and design of the elements of executive compensation do not encourage management to assume excessive risks.

25

Table of Contents

        The Compensation Committee has reviewed the elements of executive compensation to determine whether any portion of executive compensation encouraged excessive risk taking and concluded:

•

compensation is allocated among base salary and short and long-term compensation opportunities in such a way as to not encourage excessive risk-taking;



•

significant weighting towards long-term incentive compensation discourages short-term risk taking;



•

goals are appropriately set to avoid targets that, if not achieved, result in a large percentage loss of compensation; and



•

multi-year vesting of our equity awards and share ownership guidelines properly account for the time horizon of risk.

        Furthermore, as described in our Compensation Discussion and Analysis, compensation decisions include subjective considerations, which restrain the influence of formulae or objective factors on excessive risk taking.

26

Table of Contents

SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

        The following table sets forth information with respect to the beneficial ownership of our common stock by:

•

each person known to us to beneficially own more than five percent of the outstanding shares of our common stock;



•

each of our directors and executive officers; and



•

all of our directors and executive officers as a group.

        Beneficial ownership is determined in accordance with the rules of the SEC and includes voting or investment power with respect to the securities. There is no common stock subject to options that are currently exercisable or exercisable within 60 days of March 12, 2010. Percentage of beneficial ownership is based on 15,036,975 shares of common stock outstanding as of March 12, 2010.

        Unless otherwise indicated, to our knowledge, each stockholder listed below has sole voting and investment power with respect to the shares beneficially owned by the stockholder, and maintains an address c/o Main Street Capital Corporation. Our address is 1300 Post Oak Boulevard, Suite 800, Houston, Texas 77056.

27

Table of Contents

        The following table sets forth, as of March 12, 2010, the dollar range of our equity securities that is beneficially owned by each of our directors.

28

Table of Contents

AUDIT COMMITTEE REPORT

        The Audit Committee is appointed by the Board of Directors to review Main Street Capital Corporation's financial matters. Each member of the Audit Committee meets the independence requirements established by the 1940 Act and under the applicable listing standards of the Nasdaq Stock Market. The Audit Committee is responsible for the selection, engagement, compensation, retention and oversight of Main Street's independent registered public accounting firm. We are also responsible for recommending to the Board of Directors that Main Street's audited financial statements be included in its Annual Report on Form 10-K for the fiscal year.

        In making our recommendation that Main Street's financial statements be included in its Annual Report on Form 10-K for the year ended December 31, 2009, we have taken the following steps:

•

We discussed with Grant Thornton LLP, or Grant Thornton, Main Street's independent registered public accounting firm for the year ended December 31, 2009, those matters required to be discussed by Statements on Auditing Standards Nos. 61 and 90, each as amended, issued by the Auditing Standards Board of the American Institute of Certified Public Accountants, including information regarding the scope and results of the audit. These communications and discussions are intended to assist us in overseeing the financial reporting and disclosure process.



•

We conducted periodic executive sessions with Grant Thornton, with no members of Main Street's management present during those discussions. Grant Thornton did not identify any material audit issues, questions or discrepancies, other than those previously discussed with management, which were resolved to the satisfaction of all parties.



•

We received and reviewed the written disclosures and the letter from Grant Thornton required by the applicable requirements of the Public Company Accounting Oversight Board regarding Grant Thornton's communications with us concerning independence, and we discussed with Grant Thornton its independence from Main Street. We also considered whether the provision of non-audit services to Main Street is compatible with Grant Thornton's independence.



•

We determined that there were no former Grant Thornton employees, who previously participated in the Main Street audit, engaged in a financial reporting oversight role at Main Street.



•

We reviewed, and discussed with Main Street's management and Grant Thornton, Main Street's audited consolidated balance sheet at December 31, 2009, and consolidated statements of income, changes in net assets and cash flows for the year ended December 31, 2009.

        Based on the reviews and actions described above, we recommended to the Board of Directors that Main Street's audited financial statements be included in its Annual Report on Form 10-K for the year ended December 31, 2009 for filing with the Securities and Exchange Commission.

29

Table of Contents

APPROVAL TO AUTHORIZE THE SALE OF COMMON STOCK, WITH APPROVAL OF
OUR BOARD OF DIRECTORS, DURING THE NEXT YEAR AT A PRICE BELOW
NET ASSET VALUE PER SHARE

(ITEM 2)

        We are a closed-end investment company that has elected to be regulated as BDC under the 1940 Act. The 1940 Act prohibits us from selling shares of our common stock at a price below the current net asset value per share, or NAV, of such stock, with certain exceptions. One such exception would permit us to sell shares of our common stock during the next year at a price below the then current NAV if our stockholders approve such a sale and our Board of Directors makes certain determinations. Pursuant to this provision and in accordance with the requirements of the 1940 Act, we are seeking the approval of our stockholders so that we may sell or otherwise issue shares of our common stock, in one or more public or private offerings, at a price per share below our then current NAV, subject to certain conditions discussed below. If approved, the authorization would be effective for a period expiring on the earlier of the anniversary of the date of the 2010 Annual Meeting or the date of our 2011 Annual Meeting, which is expected to be held in June 2011.

        Generally, equity securities sold in public securities offerings are priced based on market prices, rather than NAV. We are seeking the approval of our common stockholders to offer and sell shares of common stock at prices that, net of underwriting discount or commissions, may be less than NAV so as to permit the flexibility in pricing that market conditions generally require.

Reasons to Offer Common Stock below NAV

        The broader fundamentals of the United States economy remain at depressed levels. Unemployment levels remain elevated and consumer fundamentals remain depressed, which has led to reductions in spending by both consumers and businesses. In the event that the United States economy remains depressed, it is likely that the financial results of small- to mid-sized companies, like those in which we invest, could experience deterioration or limited growth from current levels, which could ultimately lead to difficulty in meeting their debt service requirements and an increase in defaults. In addition, the end markets for certain of our portfolio companies' products and services have experienced negative economic trends. We are seeing reduced operating results at several portfolio companies due to the general economic difficulties. All of this has led to significant stock price volatility for capital providers such as Main Street and has made access to capital more challenging for many firms. However, for firms that continue to have access to capital, the current environment may provide more attractive investment opportunities than have been available in recent periods. Our ability to take advantage of these opportunities will depend on our access to equity capital.

        As a BDC and a regulated investment company, or RIC, for tax purposes, Main Street is dependent on its ability to raise capital through the issuance of common stock. RICs generally must distribute substantially all of their earnings to stockholders as dividends in order to achieve pass-through tax treatment, which prevents us from using those earnings to support new investments. Further, BDCs must maintain a debt to equity ratio of no more than 1:1, which requires us to finance our investments with at least as much equity as debt in the aggregate. In order to continue to build our investment portfolio, and thereby support or grow our dividends, we endeavor to periodically have access to capital through the public and private equity markets, enabling us to take advantage of favorable investment opportunities as they arise.

        Although our common stock has had a limited trading history, it has traded both at a premium and at a discount in relation to NAV. The possibilities that shares of our common stock will trade at a discount from NAV or at premiums that are unsustainable over the long term are separate and distinct from the risk that our NAV will decrease. It is not possible to predict whether any shares of our common stock issued in the future will trade at, above or below NAV. The following table lists the high

30

Table of Contents

and low sales prices for our common stock for each quarter since our initial public offering, and the sales price as a percentage of NAV. On March 12, 2010, the last reported closing sale price of our common stock on the Nasdaq Global Select Market was $15.15 per share.

        The unprecedented nature of the current credit market dislocation and uncertainty surrounding the U.S. economy has led to significant stock market volatility, particularly with respect to the stock of financial services companies. During times of increased price volatility, our common stock may periodically trade below its NAV, which is not uncommon for business development companies. As noted above, however, the current market dislocation has created, and we believe will continue to create, favorable opportunities to invest, including opportunities that, all else being equal, may increase NAV over the longer-term, even if financed with the issuance of common stock below NAV. We expect to periodically be presented with attractive opportunities that require us to make an investment commitment quickly, and we may be unable to capitalize on investment opportunities presented unless we are able to quickly raise capital. Stockholder approval of the proposal to sell shares below NAV, subject to the conditions detailed below, will provide us with the flexibility to invest in those opportunities.

        In addition, the American Recovery and Reinvestment Act of 2009 enacted in February 2009 increased the maximum amount of combined SBIC leverage (or SBIC leverage cap) to $225 million for affiliated SBIC funds from the previous SBIC leverage cap of approximately $137 million as adjusted annually based on the Consumer Price Index. Since the increase in the SBIC leverage cap applies to affiliated SBIC funds, we are required to allocate such increased borrowing capacity between our wholly-owned SBIC subsidiary, Main Street Mezzanine Fund, LP, and our majority-owned SBIC subsidiary, Main Street Capital II, LP, in which we acquired an approximate 88% limited partnership interest in January 2010. We have access to an incremental $90 million in SBIC leverage capacity, subject to the required capitalization of each SBIC fund, in addition to the $135 million of existing

31

Table of Contents

SBIC leverage at the funds. Stockholder approval of the proposal to sell shares below NAV, subject to the conditions detailed below, will provide us with flexibility in capitalizing the SBIC funds.

        Our Board of Directors believes that having the flexibility to issue our common stock below NAV in certain instances is in the best interests of our stockholders. If we were unable to access the capital markets as attractive investment opportunities arise, our ability to grow over time and continue to pay steady dividends to our stockholders could be adversely affected. It could also have the effect of forcing us to sell assets that we would not otherwise sell, and such sales could occur at times that are disadvantageous to sell.

Conditions to Sales Below NAV

        If our stockholders approve this proposal, we will only sell shares of our common stock at a price below NAV if the following conditions are met:

•

a majority of our independent directors who have no financial interest in the sale have approved the sale; and



•

a majority of such directors, who are not interested persons of Main Street, in consultation with the underwriter or underwriters of the offering if it is to be underwritten, have determined in good faith, and as of a time immediately prior to the first solicitation by us or on our behalf of firm commitments to purchase such shares or immediately prior to the issuance of such shares, that the price at which such shares are to be sold is not less than a price which closely approximates the market value of those shares, less any underwriting commission or discount.

Key Stockholder Considerations

        Before voting on this proposal or giving proxies with regard to this matter, you should consider the potentially dilutive effect of the issuance of shares of our common stock at less than NAV on the net asset value per outstanding share of common stock. Any sale of our common stock at a price below NAV would result in an immediate dilution to our existing stockholders. This dilution would include reduction in NAV as a result of the issuance of shares at a price below NAV and a proportionately greater decrease in a stockholder's interest in our earnings and assets and in voting interest than the increase in our assets resulting from such issuance. If this proposal is approved, we will be permitted to sell any amount of our common stock at any discount to our then-current NAV subject to the conditions set forth above; however, our directors will consider the potential dilutive effect of the issuance of shares when considering whether to authorize any such issuance and will act in our and our stockholders best interests in doing so.

        The 1940 Act establishes a connection between common share sale price and NAV because, when stock is sold at a sale price below NAV, the resulting increase in the number of outstanding shares is not accompanied by a proportionate increase in the net assets of the issuer. Stockholders should also consider that they will have no subscription, preferential or preemptive rights to additional shares of our common stock that may be authorized for issuance, and thus any future issuance of our common stock will dilute such stockholders' holdings of common stock as a percentage of shares outstanding to the extent stockholders do not purchase sufficient shares in the offering or otherwise to maintain their percentage interest. Further, if our current stockholders do not purchase any shares to maintain their percentage interest, regardless of whether such offering is above or below the then current NAV, their voting power will be diluted. For an illustration on the potential dilutive effect of an offering of our common stock at a price below NAV, please see the table below under the heading "Examples of Dilutive Effect of the Issuance of Shares Below NAV."

        Any sale of substantial amounts of our common stock or other securities in the open market may adversely affect the market price of our common stock and may adversely affect our ability to obtain

32

Table of Contents

future financing in the capital markets. In addition, future sales of our common stock to the public may create a potential market overhang, which is the existence of a large block of shares readily available for sale that could lead the market to discount the value of shares held by other stockholders.

Examples of Dilutive Effect of the Issuance of Shares Below NAV

        The following table illustrates the level of NAV dilution that would be experienced by a nonparticipating stockholder in three different hypothetical offerings of different sizes and levels of discount from NAV per share, although it is not possible to predict the level of market price decline that may occur. Actual sales prices and discounts may differ from the presentation below.

        The examples assume that Company XYZ has 1,000,000 common shares outstanding, $15,000,000 in total assets and $5,000,000 in total liabilities. The current NAV and NAV per share are thus $10,000,000 and $10.00. The table illustrates the dilutive effect on nonparticipating Stockholder A of (1) an offering of 50,000 shares (5% of the outstanding shares) at $9.50 per share after offering expenses and commission (a 5% discount from NAV), (2) an offering of 100,000 shares (10% of the outstanding shares) at $9.00 per share after offering expenses and commissions (a 10% discount from NAV) and (3) an offering of 200,000 shares (20% of the outstanding shares) at $8.00 per share after offering expenses and commissions (a 20% discount from NAV).