An undrafted player, Thomson began his professional career in 1969 in the International Hockey League with the Fort Wayne Komets before signing with the Blues as a free agent in 1970.

He spent the majority of his last five seasons in the Central Hockey League with the Salt Lake Golden Eagles where he was a Second and First Team All-Star in 1978 and 1979, respectively.

After spending the 1969–70 season with the IHL's Fort Wayne Komets, Thomson was invited to play summer hockey in Johannesburg, South Africa.

Thomson spent the 1971–72 season in the Western Hockey League with the Denver Spurs, a team he captained to a championship, the first of three rings he'd win during his minor-pro career.

Was taken under the wing of veterans Gary Sabourin, Red Berenson and Garry Unger early in his career with the Blues and is described as a player to took pride at both ends of the ice.