The lanky centre-back has plied his trade for a host of English clubs across various divisions. The Southampton academy product signed Manchester City in 2006. But an injury marred season sidelined the defender for most of the season.
In May 2011, Mills captained Reading in the Championship play-off Final defeat against Swansea City, where he got his name on the score-sheet.
He has also featured for national youth teams as he made eight appearances for the England U-19 side.
After spending three seasons with League One side Nottingham Forest he joined Barnsley in the 17/18 season.
He will be pairing with Uruguayan Martin Diaz at the heart of defense in Pune City.
Pune City have roped in Ian Hume from Kerala Blasters and have also managed to hold on to Brazilian forward Marcelinho.
After reaching the knock-out stage for the first time in the previous season of ISL, they decided to part ways with coach Ranko Popovic and have appointed former Dynamos coach Miguel Portugal at the helm of affairs.