Salford announced on Friday that they had agreed a fee with a club for the experienced prop and Trinity today announced he had joined them on a one-year deal.
Kopczak, 31, made his Super League debut for hometown Bradford Bulls in 2006 but it was with Huddersfield Giants where he later emerged as a front-row of genuine talent.
He helped them win the League Leaders’ Shield in 2013 before moving on to Salford where he has spent the last three years.
“I am excited and looking forward to a new challenge ahead,” said Kopczak, who retired from international duties earlier this year.
“I can’t wait to be playing with a fantastic team. It is great to be back in Yorkshire and I am really looking forward to getting stuck in, meeting the lads and getting out there playing.”
Kopczak adds to Trinity’s front-row options where they already have the likes of David Fifita, Anthony England, Craig Huby and Keegan Hirst while George King has also been recruited from Warrington Wolves.
Head coach Chris Chester said: “I am a big admirer of Craig and have been for a number of years.
“We have been chasing him for a very long time and finally the paperwork is all signed and sealed. I am delighted he has joined us for at least 12 months.”