The 2015 Man of Steel played 11 games for Penrith last season - 10 of them off the bench – after joining the Panthers midway through the year on loan from Leeds Rhinos.
Hardaker, who scored 67 tries in 155 games for Leeds, managed just one four pointer for the Panthers.
He has signed a one-year loan deal with the Castleford Tigers after NRL clubs baulked at the $525,000 transfer fee Leeds was seeking.
"There is no doubt he is an outstanding rugby league player," Tigers head coach Daryl Powell said.
