Saints have signed Wakefield prop Kyle Amor on a four year deal for a £50,000 transfer fee.
The 26-year-old has made 76 Super League appearances in his career, touching down nine times.
A powerful and destructive front-rower, Amor has made close to 3,000 metres in gains for his side this season.
Saints’ head coach Nathan Brown said: “Kyle is a young British prop forward who is already one of the best front rowers in Super League. He will add strength, size and dynamism to our pack and is a great long term recruit for the club.
Chairman Eamonn McManus added: “There was understandably a lot of competitive interest in Kyle and we are delighted to have secured him on a long term deal.
“He is another key addition to the squad which we are putting together for next season and beyond.
“There are many reasons to be excited and confident about the future.”
Amor has also played for Leeds and Whitehaven.