 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.He was one of the majority of the Texan delegation to decline to sign the 1956 Southern Manifesto opposing the desegregation of public schools ordered by the Supreme Court in "Brown v. Board of Education".