Oldham-born Mears came through the ranks at Manchester City, though only made one appearance before joining Preston North End in July 2002 for £200,000. He would stay at Deepdale for four seasons, becoming an integral member of their team before joining West Ham United for £1m in July 2006. Mears struggled to adapt to London life, eventually being loaned to Derby County, whom he eventually joined on a permanent basis in July 2007.
In 2008 Mears hit the headlines when he joined French giants Olympique Marseille on trial without, supposedly, informing his manager Paul Jewell, who later alleged that Mears had climbed out of a window at Derby's training ground in order to catch a flight to the South of France. The deal was eventually done for Mears to join Marseille on loan for the season with the prospect of a permanent deal at the end.
This did not come to pass and instead Mears joined Bolton Wanderers old boy Owen Coyle at Burnley. Mears followed Coyle to the Reebok Stadium in July 2011 in a £3m double deal with Burnley teammate Chris Eagles, however in his first week at the club he suffered a broken leg in training, which kept him out of action until January 2013. Mears' Bolton Wanderers career has been very much stop-start thus far.