Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

We hereby consent to the incorporation by reference in this Registration Statement on Form S-3 of Mercer International Inc. of our report dated February 20, 2025 relating to the financial statements and effectiveness of internal control over financial reporting, which appears in Mercer International Inc.’s Annual Report on Form 10-K for the year ended December 31, 2024. We also consent to the reference to us under the heading “Experts” in such Registration Statement.

/s/PricewaterhouseCoopers LLP

Vancouver, Canada

August 8, 2025