Exhibit 5.1

May 7, 2015

TARGA RESOURCES PARTNERS LP

1000 Louisiana, Suite 4300

Houston, Texas 77002

Ladies and Gentlemen:

We have acted as counsel for Targa Resources Partners LP, a Delaware limited partnership (the “Partnership”), with respect to certain legal matters in connection with the proposed issuance and sale from time to time by the Partnership of common units representing limited partner interests in the Partnership having an aggregate offering price of up to $1,000,000,000 (the “Units”), pursuant to that certain Equity Distribution Agreement dated May 7, 2015 (the “Distribution Agreement”) between the Partnership and Barclays Capital Inc., Citigroup Global Markets Inc., Deutsche Bank Securities Inc., Jefferies LLC, Merrill Lynch, Pierce, Fenner & Smith Incorporated, Mizuho Securities USA Inc., Morgan Stanley & Co. LLC, Raymond James & Associates, Inc., RBC Capital Markets, LLC, SunTrust Robinson Humphrey, Inc., UBS Securities LLC and Wells Fargo Securities, LLC. We have participated in the preparation of a Prospectus Supplement dated May 7, 2015 (the “Prospectus Supplement”) and the Prospectus dated April 27, 2015 (the “Prospectus”) forming part of the Registration Statement on Form S-3 (No. 333-190231) (the “Registration Statement”). The Prospectus Supplement has been filed pursuant to Rule 424(b) promulgated under the Securities Act.

In rendering the opinions set forth below, we have examined and relied upon (i) the Registration Statement, the Prospectus Supplement and the Prospectus; (ii) the First Amended and Restated Agreement of Limited Partnership of the Partnership, dated as of February 14, 2007, as amended by Amendment No. 1 to the First Amended and Restated Agreement of Limited Partnership of the Partnership dated May 13, 2008, Amendment No. 2 to the First Amended and Restated Agreement of Limited Partnership of the Partnership dated May 25, 2012, Amendment No. 3 to the First Amended and Restated Agreement of Limited Partnership of the Partnership dated February 27, 2015 and Amendment No. 4 to the First Amended and Restated Agreement of Limited Partnership of the Partnership dated February 27, 2015; (iii) the Distribution Agreement; (iv) resolutions of the Board of Directors of the general partner dated February 12, 2015; (v) resolutions of the ATM Committee of the General Partner, dated May 1, 2015; and (vi) such other certificates and other instruments and documents as we consider appropriate for purposes of the opinions hereafter expressed.

Vinson & Elkins LLP Attorneys at Law	1001 Fannin Street, Suite 2500
Abu Dhabi  Austin  Beijing  Dallas  Dubai  Hong Kong  Houston  London  Moscow	Houston, TX 77002-6760
New York  Palo Alto  Riyadh  San Francisco  Tokyo  Washington	Tel +1.713.758.2222  Fax +1.713.758.2346  www.velaw.com

May 7, 2015 Page 2

In connection with this opinion, we have assumed that all Units will be issued and sold in the manner stated in the Prospectus Supplement, the Prospectus, and the Distribution Agreement.

Based upon the foregoing and subject to the assumptions, exceptions, limitations and qualifications set forth below, we are of the opinion that the Units, when issued and delivered against payment therefore as provided in the Distribution Agreement, will be validly issued, fully paid and non-assessable, except as described in the Registration Statement, the Prospectus Supplement and the Prospectus.

The opinions expressed herein are qualified in the following respects:

A. We have assumed that (i) each document submitted to us for review is accurate and complete, each such document that is an original is authentic, each such document that is a copy conforms to an authentic original and all signatures on each such document are genuine, and (ii) each certificate from governmental officials reviewed by us is accurate, complete and authentic, and all official public records are accurate and complete.

B. This opinion is limited in all respects to the federal laws of the United States, the Delaware Revised Uniform Limited Partnership Act and the Constitution of the State of Delaware, as interpreted by the courts of the State of Delaware and of the United States. We are expressing no opinion as to the effect of the laws of any other jurisdiction.

We hereby consent to the filing of this opinion of counsel as Exhibit 5.1 to the Current Report on Form 8-K of the Partnership dated on or about the date hereof, to the incorporation by reference of this opinion of counsel into the Registration Statement and to the reference to our Firm under the heading “Legal Matters” in the Prospectus Supplement and the Prospectus. In giving this consent, we do not admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Securities and Exchange Commission issued thereunder.

Very truly yours,

/s/ VINSON & ELKINS L.L.P.

Vinson & Elkins L.L.P.