UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of report (date of earliest event reported): June 18, 2012

MARTIN MIDSTREAM PARTNERS L.P.

(Exact name of Registrant as specified in its charter)

Registrant’s telephone number, including area code: (903) 983-6200

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

Item 1.01. Entry into a Material Definitive Agreement.

On June 18, 2012, Martin Midstream Partners L.P. (the “Partnership”) entered into a definitive agreement to sell its East Texas and Northwest Louisiana natural gas gathering and processing assets owned by Prism Gas Systems I, L.P., a wholly-owned subsidiary of the Partnership, and certain other natural gas gathering and processing assets also owned by the Partnership, to CenterPoint Energy Field Services, LLC (“CEFS”), an indirect, wholly-owned subsidiary of CenterPoint Energy Inc. (“CEFS”), for $275 million (the “Divestiture”) subject to certain purchase price adjustments prior to closing. The assets to be sold include the Partnership’s 50% operating interest in the Waskom Gas Processing Company (“Waskom”). A subsidiary of CEFS owns the remaining 50% interest in Waskom. The definitive agreement contains customary representations and warranties, and indemnities. The Divestiture is subject to customary closing conditions, including antitrust approval. The Divestiture is expected to close on July 31, 2012.

Item 7.01. Regulation FD Disclosure.

On June 19, 2012, the Partnership issued a press release announcing the Divestiture. A copy of the press release is furnished as an exhibit to this Current Report on Form 8-K. The Partnership will host a conference call for analysts and investors on Tuesday, June 19, 2012 at 2:00 p.m. Central Daylight Time to discuss the Divestiture. Details regarding the call are set forth in the attached press release. Slides for the call are furnished as an exhibit to this Current Report on Form 8-K and are available on the Partnership’s website.

In accordance with General Instruction B.2 of Form 8-K, the information set forth in this Item 7.01 and in the attached Exhibits is deemed to be “furnished” and not deemed to be “filed” for purposes of the Securities Exchange Act of 1934, as amended.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.