Greenock, Renfrewshire born goalkeeper Jack Thomson began his football career with Caledonian Juniors after the First World War and played for Glasgow Benburb in 1920, from where he was signed by Third Division (South) club Bristol Rovers in May 1921, where he was understudy to their legendary custodian Jesse Whatley. He made his Football League debut at Exeter City in April 1922 and made half a dozen appearances for The Pirates before the end of the season before returning to Scottish football, joining Scottish League club Alloa Athletic in the 1922 close season.
After a single season with The Wasps, making 35 appearances, he joined Partick Thistle in 1923 and had a single season at Firhill, playing 28 times for The Jags. He joined Aberaman Athletic in 1924 before returning to Football League action, signing with close neighbours Aberdare Athletic in December that year, where he made 20 appearances for The Welshmen before signing for Brentford in May 1925, where he missed only two matches in their 1925-26 campaign. He was then signed by Third Division (South) leading club Plymouth Argyle in June 1926, who had just completed five consecutive seasons as divisional runners up, playing 7 matches during the autumn of 1926 for The Pilgrims before losing his place to Fred Craig as Argyle finished their sixth season as runners up.
Thomson moved on to Chesterfield in June 1927 where he was the incumbent during the first half of the 1927-28 campaign, making 23 appearances for The Spireites before the year end, but he joined Coventry City in January 1928 where he played just 3 matches the following month. Released by Coventry he returned to the now merged Southern League outfit Aberdare & Aberaman Athletic, Aberdare having lost their League status in 1927 when they were replace by Torquay United. Like many professional footballers at the time, Thomson had a spell in the nascent American Soccer League playing for New York Nationals later in 1928, but returned to England to join non league Nuneaton Town in 1929, his last known club before his eventual retirement.