[4] Thomson was born in Edinburgh, but began his professional career with English club, Burnley, having joined the Clarets from Scottish junior side Bo'ness United in 1959.
After a 1966–67 Fairs Cup third-round tie against Napoli, the Daily Express called him "a God in a green jersey", after Thomson kept a clean sheet over two legs in Burnley's 3–0 aggregate victory.
[5] Thomson made two appearances for the Scotland national team during a 1967 overseas tour that the Scottish Football Association decided in October 2021 to reclassify as full internationals.
He made his debut in the first game of the 1969–70 season, on 9 August 1969, in a 2–1 victory over Portsmouth at Bloomfield Road.
He played in all but two of Blackpool's 48 league and cup games that season, displacing Alan Taylor.