14th March 2018, 13:48 | StHelens
The 32-year-old will spend a ninth season with Saints in 2019, having originally joined from London Broncos in 2011.
The England and Ireland international has scored 45 tries in 220 appearances for the club and is keen to add to his medal collection with the Betfred Super League leaders.
“I’m really happy to extend my contract at the club,” McCarthy-Scarsbrook said. “I’ve been here a long time and enjoy playing in front of our great fans and with my team-mates.
“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.”