Exhibit 23(a)

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in this Registration Statement on Form S-3 of Merck & Co., Inc. of our report dated February 25, 2021 relating to the financial statements and the effectiveness of internal control over financial reporting, which appears in Merck & Co., Inc.’s Annual Report on Form 10-K for the year ended December 31, 2020. We also consent to the reference to us under the heading “Experts” in such Registration Statement.

/s/ PricewaterhouseCoopers LLP

Florham Park, NJ

March 25, 2021