Clark Wallace Thompson was born in La Crosse, Wisconsin on August 6, 1896, and moved to Oregon in 1901 with his parents, who settled in Cascade Locks. Thompson attended the common schools and the University of Oregon at Eugene. He enlisted in the United States Marine Corps during the First World War serving from 1917-1918. He remained a United States Marine Corps reservist until 1946 except when he again served on active duty during World War II from 1940-1942.

Thompson served as treasurer of the American National Insurance Company and was a Democratic member of the House of Representatives from the 7th district of Texas from 1933 to 1935, having been elected to fill the vacancy caused by the death of United States Representative Clay Stone Briggs. He later represented the Texas’s 9th district from 1947 until he retired in 1966.