Louie McCarthy-Scarsbrook has signed a one-year extension at Saints.
The 32-year-old will continue his association with the club for a ninth season.
LMS signed from London Broncos back in 2011.
He made his debut at the Magic Weekend against Wigan and has since gone on to make 220 appearances in total for the club.
The England and Ireland international has also scored 45 tries.
“I’m really happy to extend my contract at the club,” Louie said. “I’ve been here a long time and enjoy playing in front of our great fans and with my teammates.
“We last tasted success in 2014 and we want to put that right and bring silverware back to the club. We’re all working hard to do that and I’m really looking forward to the rest of this season and the next.”
Head coach Justin Holbrook added: “Louie is a very hard-working member of our team who gives us real go-forward.
“He plays and trains with high energy, a lot of enthusiasm and is very competitive, which are all good traits that I really admire about him.
“He sets a great example for the rest of the squad, as well as being a popular member of the side.”