Exhibit 5.1

August 17, 2017

STG Group, Inc.

11091 Sunset Hills Road, Suite 200
Reston, Virginia 20190

RE: STG Group, Inc. 2015 Omnibus Incentive Plan

Ladies and Gentlemen:

At your request, we have examined the Registration Statement on Form S-8 to be filed by STG Group, Inc. (the “Company”) with the Securities and Exchange Commission (the “Commission”) in connection with the registration under the Securities Act of 1933, as amended (the “Securities Act”), of an aggregate of 500,000 shares (the “Shares”) of the Common Stock, $0.0001 par value (the “Common Stock”), of the Company, which will be issuable from time to time under the Company’s 2015 Omnibus Incentive Plan (the “Plan”), as amended by the Amendment to the Company’s 2015 Omnibus Incentive Plan adopted on June 13, 2017.

As your counsel in connection with the Registration Statement, we have examined originals or copies, certified or otherwise identified to our satisfaction, of such documents, corporate records, certificates of public officials and other instruments as we have deemed necessary for the purposes of rendering this opinion and we are familiar with the proceedings taken and proposed to be taken by the Company in with the authorization, issuance and sale of the Shares.  In our examination, we have assumed the genuineness of all signatures, the authenticity of all documents submitted to us as originals and the conformity with the originals of all documents submitted to us as copies.  This opinion letter is given, and all statements herein are made, in the context of the foregoing. For the purpose of the opinion rendered below, we have assumed that in connection with the issuance of the Shares, the Company will receive consideration in an amount not less than the aggregate par value of the Shares covered by each such issuance.

Based upon and subject to the foregoing, it is our opinion that following (i) effectiveness of the Registration Statement, (ii) issuance of the Shares pursuant to the terms of the Plan, and (iii) receipt by the Company of the consideration for the Shares specified in the applicable resolutions of the Board of Directors or a duly authorized committee thereof and the Plan, the Shares will be validly issued, fully paid and nonassessable.  The opinion expressed herein is limited to the General Corporation Law of the State of Delaware, the Delaware Constitution and reported judicial decisions interpreting those laws, each as currently in effect.

This opinion letter has been prepared for use in connection with the Registration Statement. We assume no obligation to advise you of any changes in the foregoing subsequent to the effective date of the Registration Statement.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement.  In giving such consent, we do not hereby admit that we are acting within the category of persons whose consent is required under Section 7 of the Securities Act or the rules or regulations of the Commission thereunder.

Very truly yours,

/s/ Morrison & Foerster LLP