May 7, 2014

EQT Midstream Partners, LP

625 Liberty Avenue

Pittsburgh, Pennsylvania 15222

Ladies and Gentlemen:

We have acted as counsel to EQT Midstream Partners, LP, a Delaware limited partnership (the “Partnership”), in connection with the proposed offering and sale by the Partnership of an aggregate of 12,362,500 common units representing limited partner interests in the Partnership (the “Common Units”) pursuant to that certain Underwriting Agreement dated May 1, 2014 (the “Underwriting Agreement”) by and among the Partnership and EQT Midstream Services, LLC, a Delaware limited liability company and the general partner of the Partnership, on the one hand, and Barclays Capital Inc., as representative of the several underwriters named in Schedule I thereto (the “Underwriters”), on the other.

In connection with this opinion, we have examined and relied upon the accuracy of original, certified copies or photocopies of such records, agreements, certificates and other documents as we have deemed necessary or appropriate to enable us to render the opinions set out below, including (i) the registration statement on Form S-3 (Registration No. 333-189719) (the “Registration Statement”) filed by the Partnership with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Act”); (ii) the prospectus included in the Registration Statement dated July 1, 2013 (the “Base Prospectus”); (iii) the prospectus supplement to the Base Prospectus dated May 1, 2014 together with the Base Prospectus, the “Prospectus”); (iv) the Underwriting Agreement; (v) the Delaware Revised Uniform Limited Partnership Act (the “Delaware LP Act”) and (vi) the Partnership’s records and documents, certificates of representatives of the Partnership and public officials, and other instruments and documents as we deemed necessary or advisable for the purposes of this opinion.

In making our examination, we have assumed that all signatures on documents examined by us are genuine, that all documents submitted to us as originals are authentic and complete, that all documents submitted to us as certified or photostatic copies conform with the original copies of such documents and that all information submitted to us was accurate and complete.  In addition, we have relied, without independent investigation, upon the factual accuracy of the representations and warranties contained in the certificates we examined. We have also assumed that all Common Units will be issued and sold in the manner set forth in the Prospectus and the Underwriting Agreement and that any certificates for the Common Units will be duly countersigned, registered and electronically transmitted by the transfer agent and registrar for the Partnership.