[3][4] He graduated from London Catholic Central High School in 1993 and played on the football, volleyball, basketball, and track teams.

After redshirting a year, Thelwell played wide receiver on the Minnesota Golden Gophers football team from 1994 to 1997 seasons.

In 7 games in his freshman season (1994), Thelwell caught 24 passes (including 3 touchdowns) for 406 yards and had a long reception of 80.

[7] Thelwell caught a crucial, 30-yard touchdown pass on 4th-and-20 with 16 seconds left that would tie the game at 13 after the extra point.

Following his Grey Cup win, Thelwell became a free agent and elected to sign with the Calgary Stampeders on February 16, 2007.

[12][13] Due to an injury sustained by Akeem Foster, the Lions brought Thelwell out of retirement and signed him on October 25, 2011.

Thelwell also made an appearance at the William Aberhart Trojans 2007 football banquet in Calgary on November 16, 2007.