Larroyer has spent two seasons on loan at the Robins, racking up 10 tries in 51 first-team appearances.
“I’m really happy and I’ve been really looking forward to this news being announced because I love the club,” he told Rovers’ official website.
“I came in last year and they treated me very well and I always wanted to stay for a long time and be part of the project here. I can see that we are making progress and I’m sure it will be the same next season.
“I’ve not reached 100 per cent of my potential yet but I know I’m here for three more years and I can focus on what I have to work on. Next year, I want to be consistent and play well for the club to give something back.”
Robins head coach Chris Chester is delighted that the 26-year-old French international has committed to the club.
“We’re pleased to tie Kevin down to a permanent contract with the club and he’s somebody with a lot of potential to develop and improve his game,” he said.
“Last season, he was one of our most consistent performers and he’s shown his versatility this year by playing in a couple of different positions across the back row.
“He’s still got his best years ahead of him and we’re looking forward to working with him for another three seasons.”