[1] Employed as a member of the ground staff, Thompson was sent to play for two of United's feeder clubs, Woodbourne Alliance and Fulwood.
With league football suspended during World War II, Thompson became a regular player for the club's reserve team before making his first-team debut in 1941 (playing in the unofficial wartime league), becoming the club's youngest ever player to that point, being only 16 years and 103 days old.
[1] Wounded while on active duty in Germany in 1945, Thompson remained in the army after the end of the conflict, but was allowed to resume his career with Sheffield United on a part-time basis, and made his Football League debut during the 1946–47 season.
[1] Having been demobbed in 1947, Thompson finally became a full-time professional and played regularly for United for the next few seasons.
Considered to have a good amount of pace and skill, Thompson was not popular with sections of the united support who believed he lacked commitment and aggression and he was regularly barracked during games which led to Thompson asking for a transfer in 1949.