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): August 9, 2012

WILLIAMS PARTNERS L.P.

(Exact name of registrant as specified in its charter)

Registrant’s Telephone Number, Including Area Code: (918) 573-2000

Check the appropriate box below if the Form 8-K is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Item 7.01. Regulation FD Disclosure.

On August 9, 2012, Williams Partners L.P. (the “Partnership”) issued a press release announcing that it had priced the Offering (as defined below). A copy of the press release is furnished and attached as Exhibit 99.1 hereto and is incorporated herein by reference. The information furnished is not deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, is not subject to the liabilities of that section and is not deemed incorporated by reference in any filing under the Securities Act of 1933, as amended (the “Securities Act”).

Item 8.01. Other Events.

On August 9, 2012, the Partnership and Williams Partners GP LLC entered into an underwriting agreement (the “Underwriting Agreement”) with UBS Securities LLC, RBS Securities Inc., and Wells Fargo Securities, LLC, as representatives of the underwriters named in Schedule 1 thereto, with respect to the offering and sale in an underwritten public offering (the “Offering”) by the Partnership of $750 million aggregate principal amount of its 3.35% Senior Notes due 2022 (the “Notes”). The foregoing description of the Underwriting Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of the Underwriting Agreement, which is filed as Exhibit 1.1 hereto and is incorporated herein by reference.

The Offering has been registered under the Securities Act pursuant to a registration statement on Form S-3 (Registration No. 333-179471) of the Partnership (the “Registration Statement”), and the prospectus supplement dated August 9, 2012 and filed with the Securities and Exchange Commission pursuant to Rule 424(b) of the Securities Act on August 10, 2012. The Offering is expected to close on August 14, 2012 subject to customary closing conditions. A legal opinion related to the Registration Statement is also filed herewith as Exhibit 5.1.

The Notes will be issued pursuant to an Indenture (the “Base Indenture”), dated as of November 9, 2010, between the Partnership and The Bank of New York Mellon Trust Company, N.A. as trustee (the “Trustee”), as supplemented by the Third Supplemental Indenture (the “Third Supplemental Indenture”), to be dated August 14, 2012, between the Partnership and the Trustee. The Notes will be represented by a global security, which is included as an exhibit to the Third Supplemental Indenture. The form of Third Supplemental Indenture and the form of the Notes are filed as Exhibits to this Current Report on Form 8-K and are incorporated herein by reference.

The Partnership intends to use the net proceeds from the Offering to repay outstanding borrowings under its senior unsecured credit facility and for general partnership purposes.

Item 9.01. Financial Statements and Exhibits.

SIGNATURE

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.

DATED: August 13, 2012

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