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): May 31, 2017

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 filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (17 CFR 230.405) or Rule 12b-2 of the Securities Exchange Act of 1934 (17 CFR 240.12b-2).

Emerging growth company  ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☐

Item 7.01. Regulation FD Disclosure.

On May 31, 2017, 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”).

On May 31, 2017, the Partnership and WPZ GP LLC entered into an underwriting agreement (the “Underwriting Agreement”) with Deutsche Bank Securities Inc., Merrill Lynch, Pierce, Fenner & Smith Incorporated and RBC Capital Markets, 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 $1,450,000,000 aggregate principal amount of its 3.750% Senior Notes due 2027 (the “Notes”). The Underwriting Agreement is filed as Exhibit 1.1 hereto.

The Offering has been registered under the Securities Act pursuant to a registration statement on Form S-3 (Registration No. 333-202282) of the Partnership (the “Registration Statement”), and the prospectus supplement dated May 31, 2017 and filed with the Securities and Exchange Commission pursuant to Rule 424(b) of the Securities Act on June 2, 2017. The Offering is expected to close on June 5, 2017. A legal opinion related to the Registration Statement is filed herewith as Exhibit 5.1.

The Notes will be issued pursuant to an 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 Ninth Supplemental Indenture (the “Supplemental Indenture”), to be dated June 5, 2017, between the Partnership and the Trustee. The Notes will be represented by a global security, which will be included as an exhibit to the Supplemental Indenture. The form of 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.

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: June 5, 2017

EXHIBIT INDEX