Contracted until the end of next season, the Knights confirmed on Tuesday they had tabled a one-year extension for Barnett to keep him at the club.

However, that has not been taken up, with the 28-year-old to instead link with Nathan Brown's Warriors when they return home in 2023 on a three-year deal.

"Barnett's management requested approval to negotiate with other parties," Newcastle said in a statement.

"The Newcastle Knights granted permission based on the exceptional service Barnett has given to the club and the respect he has earnt since joining the Knights in June 2016.

"Barnett has a remaining year on his current contract and the Knights offered an extension into 2024.

"However, both parties have agreed the decision to accept the other offer is the right decision for Mitch, his wife Clare and newborn son Nate."

Barnett is due back from suspension in Magic Round against Canterbury, after copping six games on the sidelines for his elbow to the jaw of Penrith's Chris Smith.

Barnett is the Warriors' third major signing for 2023, after Marata Niukore and Dylan Walker.

In doing so, he will link back up with Brown after the coach brought him home from Canberra to the Hunter region in 2016.

"The Warriors presented me with an opportunity to further my game," Barnett said.

"I have personal goals of playing representative football and I am also looking forward to working with Brownie again.

"The Warriors impressed me on and off the field which made my decision easier."

Australian Associated Press