Upon the U.S. entry into World War I in 1917, Cooper enlisted in the Second Tennessee Infantry, National Guard, and was commissioned a first lieutenant. Later he was transferred, with his company, to Co K, 119th Infantry, Thirtieth Division, and served in France and Belgium. On July 9, 1918, he was promoted to captain and served as regimentaladjutant until discharged from the army on April 2, 1919. After the war he resumed the practice of law in Dyersburg.
Cooper was a member of the city council and city attorney from 1920 to 1928, and was elected department commander of the American Legion of Tennessee in 1921.
Elected as a Democrat to the 71st, and to the fourteen succeeding, Congresses, Cooper served from March 4, 1929, until his death.[2] He served as chairman of the U.S. House Committee on Ways and Means (84th and 85th Congresses), and on the Joint Committee on Internal Revenue Taxation (Eighty-fifth Congress).[3]