Zak Hardaker will play for Wigan once his drugs ban expires in November.
The 26 year-old is serving a 14-month suspension imposed by UK Anti-Doping after testing positive for cocaine. The suspension was confirmed in April but back-dated to September 2017, when he took the test.
He was sacked by his club Castleford after they were informed of the test.
Wigan confirmed he had signed a four-year deal and will be free to join the club officially on November 8. The club said he would be permitted to train with them two months before that.
The club's chairman Ian Lenagan said: "This wasn't a decision that we made lightly. We recognise the serious nature of this incident and our choice in offering this opportunity should not be seen as condoning his actions in any way."
Lenagan added: "We had extensive conversations with Zak and his family before making our offer.
"We encountered a man who, after eight months of reflection, openly admits that he has made a series of significantly poor decisions over the past few years. Crucially, we also saw someone who recognises that this is the final opportunity to focus on delivering the achievements his talent should generate."
Hardaker has won the Super League Grand Final and Challenge Cup twice each, all with Leeds.
He won the Super League's Man of Steel award in 2015.
Hardaker joined Castleford initially on loan in the autumn of 2016 before making the move permanent in June 2017.
He was left out of the Tigers' Grand Final squad in October 2017 to face his old club Leeds after the adverse drugs test came to light.