Lunt, 28, has put pen to paper on a four-year deal at the KC Lightstream Stadium, having initially joined from Huddersfield on loan earlier this season.
He said: “I’ve had a great time since joining the club earlier this season and I’m delighted to sign a new long-term contract.
“The fans have been fantastic with me ever since I came and I can’t thank them enough for that. They’re crackers but they’ve really made me feel welcome, as have the players and the coaching staff.
“I’m really pleased to get my future secured at such a great club and I feel like I’m starting to get back to my best form here at Hull Kingston Rovers. I know there is plenty more to come from me but I’m really enjoying my rugby again and that made staying here for another four years an easy decision to make.
“I wanted to get the new contract sorted before the cup final on Saturday and now I can concentrate on the game. I’ve been on the losing team at Wembley twice in my career and I’d love nothing more than to be picking up that trophy and giving it a big kiss this weekend.
“It would mean the world to me and those boys in the changing room, as well as to the fans and to the club.”
Head coach Chris Chester added: “Signing up Shaun to a new contact was one of our main aims for next season and it’s been a smooth process dealing with Lunty and his agent. He wanted to stay and we wanted to keep him so we’re thrilled to get the deal over the line.
“It’s a real statement of intent from the club to tie down a player of Shaun’s calibre on a long-term contract. He’s coming into the prime of his career and he’s somebody with a pedigree of playing well in big games.
“He’s an experienced player who’s played in Challenge Cup Finals and Grand Finals and he’s fitted in really well around the club, so we’re really looking forward to having him on board for another four years.”