Mills originally started out his career at Southampton, but enjoyed loan spells at Coventry City and Bournemouth to gain further experience, during which he caught the eye of scouts at Manchester City, who signed him on a deal in January 2006.
Having made two Premier League appearances for City against Chelsea and Wigan Athletic, loan spells at Colchester United and Doncaster Rovers followed for Mills before he made the permanent switch to the Keepmoat Stadium in the summer of 2008.
However, the defender was on the move again after just a single season at Doncaster, joining Reading in a £2million deal in August 2009.
Captaining the Royals to the 2011 Championship Play-Off Final, Mills scored scoring a header as Reading were denied promotion to the top-flight by Swansea City, who won the game at Wembley 4-2.
Mills joined Leicester City later that summer and was immediately handed the captain’s armband, but after just 12 months at King Power Stadium he was on the move again, this time signing for Wanderers.