UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM S-8

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

TRIANGLE CAPITAL CORPORATION

(Exact name of registrant as specified in its charter)

TRIANGLE CAPITAL CORPORATION AMENDED AND RESTATED 2007 EQUITY INCENTIVE PLAN

(Full title of the plan)

Garland S. Tucker, III

Chairman, President and Chief Executive Officer

3700 Glenwood Avenue, Suite 530

Raleigh, North Carolina 27612

(Name and address of agent for service)

(919) 719-4770

(Telephone number, including area code, of agent for service)

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

CALCULATION OF REGISTRATION FEE

EXPLANATORY NOTE

This Registration Statement on Form S-8 hereby registers 1,500,000 additional shares of Common Stock for issuance under Triangle Capital Corporation’s (the “Company”) Amended and Restated 2007 Equity Incentive Plan (the “Amended and Restated Plan”). Previously, 900,000 shares of Common Stock under the Amended and Restated Plan were registered on April 3, 2007 (File No. 333-141827). At the Company’s annual meeting of stockholders on May 2, 2012, the stockholders approved an amendment to the Amended and Restated Plan to increase the number of shares of Common Stock issuable under the Amended and Restated Plan by 1,500,000 shares of Common Stock. The Amended and Restated Plan allows the Company, under the direction of the Compensation Committee of the Board of Directors, to make grants of restricted stock other stock-based awards to the Company’s directors and certain of its employees.

PART I

INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

Information required by Part I to be contained in the Section 10(a) prospectus is omitted from this Registration Statement in accordance with Rule 428 under the Securities Act of 1933, as amended, and the Note to Part I of Form S-8.

PART II

INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference.

The following documents filed with the Securities and Exchange Commission (the “Commission”) by the Company, are incorporated as of their respective dates in this Registration Statement by reference:

All documents filed by the Company pursuant to Section 13(a), 13(c) 14 or 15(d) of the Exchange Act after the date of this Registration Statement and prior to the filing of a post-effective amendment which indicates that all securities offered have been sold or which deregisters all securities then remaining unsold, shall be deemed incorporated by reference in this Registration Statement and to be a part hereof from the date of filing such documents.

Item 4. Description of Securities.

Not applicable.

Item 5. Interests of Named Experts and Counsel.

Not applicable.

Item 6. Indemnification of Directors and Officers.

Maryland law permits a Maryland corporation to include in its charter a provision limiting the liability of its directors and officers to the corporation and its stockholders for money damages except for liability resulting from (a) actual receipt of an improper benefit or profit in money, property or services or (b) active and deliberate dishonesty established by a final judgment as being material to the cause of action. The Company’s charter contains such a provision that eliminates directors’ and officers’ liability to the maximum extent permitted by Maryland law, subject to the requirements of the 1940 Act.

The Company’s charter authorizes the Company, to the maximum extent permitted by Maryland law and subject to the requirements of the 1940 Act, to indemnify any present or former director or officer or any individual who, while a director or officer and at the Company’s request, serves or has served another corporation, partnership, joint venture, trust, employee benefit plan or other enterprise as a director, officer, partner or trustee, from and against any

claim or liability to which such person may become subject or which such person may incur by reason of his or her service in any such capacity, except with respect to any matter as to which he or she is finally adjudicated in any proceeding not to have acted in good faith in the reasonable belief that his or her action was in the Company’s best interest.

The Company’s bylaws obligate the Company, to the maximum extent permitted by Maryland law and subject to the requirements of the 1940 Act, to indemnify any present or former director or officer or any individual who, while a director or officer and at the Company’s request, serves or has served another corporation, partnership, joint venture, trust, employee benefit plan or other enterprise as a director, officer, partner or trustee and who is made, or threatened to be made, a party to the proceeding by reason of his or her service in any such capacity from and against any claim or liability to which that person may become subject or which that person may incur by reason of his or her service in any such capacity. The Company’s bylaws also require the Company, to the maximum extent permitted by Maryland law, without requiring a preliminary determination of the ultimate entitlement to indemnification, to pay or reimburse reasonable expenses incurred by any such indemnified person in advance of the final disposition of a proceeding.

Maryland law requires a corporation (unless its charter provides otherwise, which the Company’s charter does not) to indemnify a director or officer who has been successful in the defense of any proceeding to which he or she is made, or threatened to be made, a party by reason of his or her service in that capacity. Maryland law permits a corporation to indemnify its present and former directors and officers, among others, against judgments, penalties, fines, settlements and reasonable expenses actually incurred by them in connection with any proceeding to which they may be made, or threatened to be made, a party by reason of their service in those or other capacities unless it is established that (a) the act or omission of the director or officer was material to the matter giving rise to the proceeding and (1) was committed in bad faith or (2) was the result of active and deliberate dishonesty, (b) the director or officer actually received an improper personal benefit in money, property or services or (c) in the case of any criminal proceeding, the director or officer had reasonable cause to believe that the act or omission was unlawful. However, under Maryland law, a Maryland corporation may not indemnify for an adverse judgment in a suit by or in the right of the corporation or for a judgment of liability on the basis that a personal benefit was improperly received, unless in either case a court orders indemnification, and then only for expenses. In addition, Maryland law permits a corporation to advance reasonable expenses to a director or officer upon the corporation’s receipt of (a) a written affirmation by the director or officer of his or her good faith belief that he or she has met the standard of conduct necessary for indemnification by the corporation and (b) a written undertaking by him or her or on his or her behalf to repay the amount paid or reimbursed by the corporation if it is ultimately determined that the standard of conduct was not met.

The Company has purchased directors’ and officers’ insurance policies covering our directors and officers and the Company for any acts and omissions committed, attempted or allegedly committed by any director or officer during the policy period. The policy is subject to customary exclusions.

Item 7. Exemption from Registration Claimed.

Not applicable.

Item 8. Exhibits.

Item 9. Undertakings.

Provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) do not apply to information required to be included in a post-effective amendment by those paragraphs that is contained in reports filed with or furnished to the Commission by the registrant pursuant to Section 13 or Section 15(d) of the Exchange Act that are incorporated by reference in the Registration Statement.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Raleigh, State of North Carolina, on this 4^th day of January, 2013.

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that each person whose signature appears below constitutes and appoints Garland S. Tucker, III, Steven C. Lilly and C. Robert Knox, Jr., and each of them, his true and lawful attorneys-in-fact and agents, with full power of substitution and resubstitution, for him and in his name, place and stead, in any and all capacities, to sign any and all amendments (including post-effective amendments) to this Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents, or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed by the following person in the capacities and on the dates indicated:

EXHIBIT INDEX