Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in the Registration Statements on Form S-3 (No.333-289440) and Form S-8 (No. 333-287834) of Mercer International Inc. of our report dated February 12, 2026 relating to the financial statements and the effectiveness of internal control over financial reporting, which appears in this Form 10-K.

/s/PricewaterhouseCoopers LLP

Chartered Professional Accountants

Vancouver, Canada

February 12, 2026