Greg Stewart joined Blues from Scottish Premier League side Dundee in August 2016 on a three-year deal for an undisclosed fee.
Stewart, who is a former Rangers and Hearts academy product, can play any of the front four positions.
The Stirling-born player made 84 appearances for The Dark Blues after joining from Cowdenbeath in 2014, scoring 32 goals.
Stewart was selected for the PFA Scotland Player of the Year shortlist in each of his two seasons at Dens Park.
His debut for Blues came in the in the 1-1 Championship draw away at Wigan Athletic on 16 August 2016.