Born in Spafford, New York, Knapp received a Bachelor of Arts degree from Wesleyan University in 1868 and read law to enter the bar in 1869.

[1] Under the Erdman Act as ex officio mediator, he assisted in the work of settlement of numerous disputes between the public and the railroads.

He was confirmed by the United States Senate on December 20, 1910, and received his commission the same day.

Knapp was reassigned by operation of law to the United States Court of Appeals for the Fourth Circuit on January 1, 1916, to a new seat authorized by 36 Stat.

His service terminated on February 10, 1923, due to his death in Washington, D.C.[1] Knapp was appointed a mediator for two years from March 4, 1911, becoming member of the Board of Mediation and Conciliation under the Newlands Act in 1913, by appointment of President Woodrow Wilson.