[5] He is widely recognised as one of the club's greatest imports, and is considered a fans' favourite due to his consistency and commitment as well as his community contributions off the pitch.

After Canterbury-Bankstown failed to make the NRL finals series in 2011 they agreed to release him from the remainder of his playing contract to allow him to take up a two-year deal with the Castleford Tigers in the European Super League.

[11] In July 2013, Millington signed a one-year contract extension with the Tigers, with head coach Daryl Powell labelling him "a stand-out performer".

[16] In 2016, due to the Tigers' extensive injury list, Millington displayed his positional versatility by starting 3 games in the halves for Castleford.

Millington played a crucial role in the 2017 Castleford campaign, contributing to the Tigers' first League Leaders' Shield and Grand Final appearance.

[23] Following his excellent start to the 2020 Super League season, Castleford head coach Powell stated that "this year he's at a different level" and expressed his intention to open further contract talks with Millington.