EXHIBIT 5.1

Tel +1.713.758.2222 Fax 713.758.2346

November 4, 2016

Western Gas Equity Partners, LP

1201 Lake Robbins Drive

The Woodlands, Texas 77380

Ladies and Gentlemen:

We have acted as counsel for Western Gas Equity Partners, LP, a Delaware limited partnership (the “Partnership”), in connection with the preparation of the Registration Statement on Form S-3 (the “Registration Statement”) filed on the date hereof with the United States Securities and Exchange Commission (the “Commission”) in connection with the registration by the Partnership under the Securities Act of 1933, as amended (the “Securities Act”), of the offer and sale by the selling unitholder named in the Registration Statement from time to time, pursuant to Rule 415 under the Securities Act, of up to an aggregate of 50,000,000 common units representing limited partner interests in the Partnership (the “Common Units”). We have also participated in the preparation of the Prospectus (the “Prospectus”) contained in the Registration Statement to which this opinion is an exhibit.

In connection with the rendering of the opinions hereinafter set forth, we have examined (i) executed copies of the organizational documents of the Partnership and Western Gas Equity Holdings, LLC (the “General Partner”); (ii) the Registration Statement, including the Prospectus; (iii) resolutions of the Board of Directors of the General Partner; and (iv) such other certificates, statutes and other instruments and documents as we considered appropriate for purposes of the opinions hereafter expressed. In addition, we reviewed such questions of law as we considered appropriate.

In connection with rendering the opinions set forth below, we have assumed that (i) all information contained in all documents reviewed by us is true and correct, (ii) all signatures on all documents examined by us are genuine, (iii) all documents submitted to us as originals are authentic and complete and all documents submitted to us as copies conform to the originals of those documents, (iv) the Registration Statement, and any amendments thereto (including post-effective amendments), will be effective and comply with all applicable laws, (v) all Common Units will be offered and sold in compliance with applicable federal and state securities laws and in the manner specified in the Registration Statement and any applicable prospectus supplement (“Prospectus Supplement”), (vi) one or more Prospectus Supplements may have been prepared and filed with the Commission describing the Common Units offered thereby and will comply with all applicable laws and (vii) a definitive purchase, underwriting or similar

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

November 4, 2016 Page 2

agreement with respect to any Common Units offered will have been duly authorized and validly executed and delivered by the Partnership and the other parties thereto.

Based on the foregoing, and subject to the assumptions, qualifications, limitations and exceptions set forth herein, we are of the opinion that the Common Units are validly issued, fully paid (to the extent required under the First Amended and Restated Agreement of Limited Partnership of the Partnership) and non-assessable (except as such non-assessability may be affected by Section 17-607 or 17-804 of the Delaware Revised Uniform Limited Partnership Act (the “DRULPA”) and as described in the Prospectus and any applicable Prospectus Supplement).

The foregoing opinion is limited to the DRULPA (including the applicable provisions of the Delaware Constitution and the reported judicial decisions interpreting these laws) and the federal laws of the United States of America. We are expressing no opinion as to the effect of the laws of any other jurisdiction, domestic or foreign.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement and to the use of our name in the Prospectus forming a part of the Registration Statement under the caption “Legal Matters.” 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.

Very truly yours,

/s/ Vinson & Elkins L.L.P.

Vinson & Elkins L.L.P.