Williams is returning to the club where he began his career, and has signed a two-year deal with the NRL outfit.
The 23-year-old joined the Catalans from St George-Illawarra Dragons halfway through the current campaign. He is relishing returning to Australia and working with coach Ricky Stuart.
“The Raiders are my home club with some of my best mates and a club I’ve always wanted to see successful so I’d love to be a part of any success we have in the future,” he said.
“I’m looking forward to the opportunity to work hard to try and earn a place in the team next season.
“I have heard plenty of positive things from the boys about Ricky and the coaching staff and the changes that Ricky has implemented. He’s a club legend and one of the best ever halfbacks, so I can certainly look to improve working under him.
“I can’t wait to be back with the Green Machine, it’s a place I’ve always called home and wearing the green has always been what I feel most comfortable with.
“There’s some great talent at the club who I’ve played with before and some more coming through the ranks and I want to be part of a squad of players who can bring us back to the top.”
“Sam is a gifted playmaker who we believe will be a valuable asset for our squad,” added Raiders recruitment and high performance manager David Hamilto.
“He’s a really strong organising halfback who knows how to get a team around the park and we know his competitive nature and willingness to succeed will make him a front runner to be in the NRL team in 2015.