In college, he was a star athlete for the Oklahoma Sooners under legendary coach Bud Wilkinson. He led the Sooners in scoring during both the 1956 and '57 seasons, while also leading the nation in the category during the 1956 season. He helped lead the Sooners to back-to-back national championships in 1955 and 1956. He was an All-Conference selection his junior and senior years and was a consensus All-American his senior year. He also finished in ninth place in the Heisman Trophy balloting that season (the award was won by John David Crow that year).
In the 1958 NFL Draft, Thomas was selected by the Los Angeles Rams in the second round. He played for the Rams for four seasons before being traded to the Pittsburgh Steelers where he played for another seven years and finished his career. He was selected to the Pro Bowl after the 1963 NFL season.