He was an attorney with the Real Estate Appraisal Division of Shell Oil Company from 1929 to 1931.

Harper was a major in the United States Army Air Corps from 1942 to 1945.

[Note 1] The Senate still did not confirm his nomination, so his service terminated on June 22, 1948.

The Senate finally confirmed Harper on January 31, 1949, and he received his commission on February 2, 1949.

He served as Chief Judge of the Eastern District from 1959 to 1971, and he was a member of the Judicial Conference of the United States from 1965 to 1971.