Roby, 28, is now likely to go through his career as a one club man, having made his debut for Saints back in 2004, going on to make 280 appearances.
Chairman Eamonn McManus said: “This is a huge and timely boost both for the Club and, just as importantly, for Super League. Understandably, as one of the best hookers in the world, James attracted considerable interest from the NRL but ultimately showed continued loyalty to St Helens and to the English game.
“It is now his testimonial year so I would hope that our fans and rugby league fans generally, show their support for his testimonial game and events in recognition of his continued loyalty and commitment to our club and to our league.
“He has been St Helens‘ stand out performer for the last decade and is one of English Rugby League’s national treasures – it’s more than gratifying to know that he has committed long term to us and that we can continue to build the next generation of Saints players around him.”
Roby, who was the first player to score a try at the new Wembley Stadium during the Challenge Cup final win over Catalan in 2007, has won Super League, Challenge Cup (three times) and the World Club Challenge during his time with the club.
He said: “It’s great to commit to a long term deal with St Helens. I signed with them immediately after school and am now entering my testimonial season. It is more than fulfilling to spend my entire career with such a great club.”