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): April 29, 2014

REGENCY ENERGY PARTNERS LP

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (214) 750-1771

(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):

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

On April 30, 2014, Regency Energy Partners LP (the “Partnership”) issued a press release announcing that the Partnership and Eagle Rock Energy Partners, L.P. (“Eagle Rock”) certified substantial compliance with the Federal Trade Commission (the “FTC”) in connection with the FTC’s review of the proposed contribution of Eagle Rock’s midstream business to the Partnership (the “Midstream Contribution”) and that the Partnership and Eagle Rock agreed to extend the FTC’s review period until June 30, 2014 unless the FTC completes its investigation earlier.

Additionally, on April 29, 2014, Eagle Rock’s common unitholders voted to approve the Midstream Contribution. A full copy of the press release is filed as Exhibit 99.1 hereto and is incorporated herein by reference.

(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.

EXHIBIT INDEX