Exhibit 5.1

July 28, 2017

Clearwater Paper Corporation

601 West Riverdale Avenue, Suite 1100

Spokane, WA 99201

Re: Registration Statement on Form S-8

Ladies and Gentlemen:

Reference is made to the Registration Statement on Form S-8 (the “Registration Statement”) to be filed by Clearwater Paper Corporation, a Delaware corporation (the “Company”), with the Securities and Exchange Commission under the Securities Act of 1933, as amended, relating to 2,100,000 shares of Common Stock issuable pursuant to the Clearwater Paper Corporation 2017 Stock Incentive Plan (the “Incentive Plan”).

It is my opinion that such shares Common Stock of the Company, when issued and sold in accordance with the Incentive Plan, will be legally issued, fully paid and nonassessable.

I hereby consent to the filing of this opinion with the Securities and Exchange Commission as Exhibit 5.1 to the Registration Statement.

Very truly yours,

/s/ Michael S. Gadd

Michael S. Gadd

Vice President, General Counsel and Corporate Secretary