The 26-year-old has agreed a deal that will keep him at the Totally Wicked Stadium until the end of the 2019 season.
“Jonny is a classy player and I’m delighted he has committed his future to us,” Saints Head Coach Justin Holbrook said. “He is an integral to the squad and not only offers us versatility and quality but is an example to the younger players coming through the system.”
Jonny signed into the Saints’ system from Orrell St James and made his first team debut in 2009 at Wakefield.
He cemented his place in the first team squad during the 2011 season and has gone on to make 147 appearances for the club, scoring 468 points.
His form in 2016 also saw him called up for England’s 2016 Four Nations campaign and, after being selected in the EPS, is expected to feature in this year’s World Cup.
Jonny added: “I am more than happy to sign this contract. I have grown up loving and supporting the club. At heart I am a fan of the Saints and want the best for the club in every way possible.
“I am delighted and hopefully I can do some good things over the next two years.
“I was aware that there was other interest in me but the club is always at the centre of my heart and has supported me through long periods of injury in recent years. I am delighted and made up to remain here.”