Johnston began his professional career as a teenager with St Johnstone, playing over 200 times for the Perth club including the semi-final of the 1988–89 Scottish Cup when the part-time, second-tier side took champions-elect Rangers to a replay,[3][4] and a match described as 'McDiarmid Park's greatest' when closest challengers Airdrieonians were defeated to virtually confirm the 1989–90 Scottish First Division title and promotion to the Premier Division.
He stayed at Somerset Park for less than a season before switching to Partick Thistle in a swap deal involving Cammy Duncan in March 1991.
After departing from Firhill, he had short spells with Ballymena United in Northern Ireland and Stranraer in Scotland,[1] before crossing the Irish Sea for a longer period, playing in the Irish League for Glenavon – where he had a car park fistfight with opponent Pat McAllister,[8] scored in the 1995–96 UEFA Cup[9] and won the Irish Cup in 1997 – and Coleraine, and in the League of Ireland for Finn Harps.
[1] After retiring from playing, he later managed Neilston Juniors for three years[11] (leading them to the SJFA West Region Premiership) and was assistant to Mark Cameron at Arthurlie.
[12][13] His younger brother Allan (a Scottish international with 18 caps) and nephew Max also played professionally.