Louis McCarthy-Scarsbook made his England debut in 2008
St Helens have signed Harlequins prop Louie McCarthy-Scarsbrook on a four-year deal that will start next season.
The 24-year-old England international came through the Quins youth scheme and made his senior debut in 2005.
He has made 90 appearances for the London side and will play his last game in Friday's clash with Warrington.
McCarthy-Scarsbrook said: "St Helens are entering an exciting time in their history and to be a part of that was a great pull."
He continued: "Not only will they have a new stadium in 2012 but the quality of the players already in the squad means they will be challenging on all fronts.
"I am looking forward to linking up with my new teammates and continuing to learn under Royce Simmons.
"I would like to thank Quins for giving me the chance to play rugby league and I have enjoyed my time there. The fans and players have been excellent with me and I wish them all well in the future."
Saints chief executive Tony Colquitt added: "Understandably, there were a number of clubs chasing a player of Louie's calibre and we're pleased he decided to join the Saints.
"At the age of 24, he will continue to develop and we're looking forward to him joining up with the rest of the squad in November as we prepare for the 2011 season."