Bachelor, Yale University, 1950. Juris Doctor, University Arkansas, 1956.
A graduate of Sheridan High School, Thornton earned a degree in political science from Yale University and, later, a law degree from the University of Arkansas. He served in the United States Navy during the Korean War, earning the rank of lieutenant. Thornton returned to law school after returning from of Korea.
Obtaining his law degree in 1956.
After election as Arkansas Attorney General in 1970, he was elected to Congress as a Democrat in 1972. He defeated fellow Democrat Richard South. Arnold of Texarkana in the primary.
Thornton went on to serve three terms in the House. Thornton did not run for a fourth term in the House.
Instead, he ran for the Senate, but narrowly lost in the Democratic primary to Governor David Pryor.
Pryor then defeated a liberal Republican, William T. Kelly, in the general election. After his defeat in the Senate race, Thornton became involved in education, serving as President of Arkansas State University and then the University of Arkansas System from 1984 to 1990. Thornton left Congress after another three terms, having retired in January 1997.
Thornton served as a justice of the Arkansas Supreme Court from 1997 to 2005.
After retiring from the court, he became the first public service fellow for the William Bowen School of Law at the University of Arkansas in Little Rock. In 2009, he became the first chairman of the Arkansas Lottery Commission, which operates the Arkansas Scholarship Lottery.
Chairman president's development council Harding College, Searcy, Arkansas, 1971-1973. Served with United States Navy, 1951-1954, Korea. Member American Association for the Advancement of Science (Chairman of Commission on science, engineering and public policy 1980).
Married Betty Jo Mann, January 27, 1956. Children: Nancy, Mary Jo, Stephanie.