Rejecting the opportunity of an international trial game at Methil, Gallacher made his Queen of the South debut aged 17 against St Cuthbert Wanderers on 29 January 1921. Gallacher scored four goals in a 7–0 victory. The Herald and Courier wrote after the game, "Gallacher was the pick of the front line. He is only a young player but knows all that is required of him in the centre. He gathers the ball to perfection and possesses a first time shot of a deadly nature. His four goals were all well taken and it was not his fault that he did not have more". The contract was waiting for Gallacher after the game.