Exhibit 15.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in the Registration Statements on Form S-8 (No. 333-88966, 333-100388 and 333-162702) of GlaxoSmithKline plc of our report dated 17 March 2017 relating to the financial statements and the effectiveness of internal control over financial reporting, which appears in this Form 20-F.

/s/ PricewaterhouseCoopers LLP    

PricewaterhouseCoopers LLP

London, United Kingdom

17 March 2017