 On 20 June 2012, Colbeck signed a two-year deal with Grimsby Town.Colbeck scored his first goal for Grimsby on 27 August 2012 against Mansfield Town, scoring the third goal of the game on 61 minutes, after good link up play between Greg Pearson who crossed into the box, the ball bouncing off strike partner Andy Cook for Colbeck to side-foot it into the top corner, the game finishing a 4–1 to the Grimsby.On Boxing Day 2012, Colbeck provided 3 assists and scored directly from a corner in the 4–1 Lincolnshire derby win over Lincoln City at Sincil Bank.