[1][2] Thornton was selected originally by the Cleveland Browns of the National Football League in the 1961 NFL draft out of Northwestern University, where he starred at quarterback.
[3] The Browns immediately traded his rights to the St. Louis Cardinals, but Thornton went to play in Canada, where he starred mostly as a defensive back.
However, he was an important cog as cornerback on the 1962 team, after intercepting 4 passes and returning one for a touchdown, recovering two fumbles, and blocking a kick during the regular season.
In 1964, he missed most of the season due to an injury, but recovered well in 1965, when he starred again at defensive back and wide receiver, his team making it to the 53rd Grey Cup, the nearly supernatural "Wind Bowl", this time losing to Hamilton.
In April 1976, Thornton was hired as athletic director and head football coach at Southwestern at Memphis—now known as Rhodes College.