During his 9-year career, Thelen rushed for 8,463 yards on 1,530 carries and scored 47 touchdowns. His best years were 1959 to 1961, when he rushed for over 1,000 yards for 3 straight years. He was the CFL’s leading rusher in 1960 with 1407 yards (5.7 yards/rush) and the eastern conference leader in 1959 and 1965. In one game in 1960, he carried 33 times for 209 yards against the Toronto Argonauts. That year, he was part of the 48th Grey Cup winning team. In 1965, Thelen was replaced by Bo Scott and traded to the Toronto Argonauts, playing his final two years with them.