Bolton Wanderers struck a deal with Leicester City to bring Matt Mills to Macron Stadium on a three-year contract on July 4, 2012.
The central defender, 25, becomes Wanderers' second signing of the summer transfer window after the two clubs agreed an undisclosed fee.
Throughout the 2011/12 campaign, Mills made 31 appearances for Leicester having been recruited from Reading a year previously.
During his two-year spell with the Royals, Mills had been a virtual ever-present, clocking up 75 games between the summers of 2009 and 2011.
Just over 12 months earlier he helped Reading to reach the Championship play-off final, scoring a header as they were denied promotion to the top-flight by Swansea, who won the game at Wembley 4-2.
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.
After a single season at Doncaster, Reading moved to secure Mills' services for £2million in 2009.