24-year-old Mata’utia played 124 NRL matches for the Knights after captaining the club at just 20 years of age.
“Sione shares a wonderful history with the Knights, he’s a local junior who made an NRL and Kangaroos debut in the same year, becoming the youngest player to achieve this milestone,” said head coach Adam O’Brien on the club website.
“He’s been a great servant for the club, in both good and tough times, while his attitude and commitment both on and off the field has always been outstanding.
“We are really pleased to see him get an opportunity to extend his career in England and the chance to travel with his family.
“He is a great young man, who leaves the club with the highest regard.
“Everyone at the Knights wishes him all the best for the future.”