The former Leeds, Hull and Bradford forward is an ex-England international with over 250 first team appearances to his name in the top flight.
Having initially signed for the club earlier this season, Scruton has committed to the Robins despite the drop to the Kingstone Press Championship and will link up with his new teammates for pre-season training later this month.
The 6ft 1in, 16-stone forward, who was part of the 2008 World Club Challenge-winning Leeds Rhinos side, told the club website: “Everybody’s objective and goal at the club has changed now since I first signed but there’s still a job to do and I’m keen to help out now and get us back to where we belong.
“I’ve been reading about all the season ticket sales and things like that so the Hull KR fans seem like a great bunch and I just want to get out there and impress them all.
“I’ll be one of the more experienced campaigners in the squad so I’ll be looking to bring a bit of that experience and add some impact.
“It’s always been my role to get the team going forward and that won’t change.
“It’s a tough league now is the Championship so hopefully I can add some physicality to the pack and help out where I can.”
Head of Rugby Jamie Peacock said: “Nick is another example of a player who has shown his loyalty to the club. He had the opportunity to look for another deal in Super League but he’s made a commitment to the club and he wants to see that through.
“We need tough, uncompromising players as part of the squad for next and he is certainly that.
“He’s got a great work ethic both on and off the pitch and he’ll set a real example for some of the younger forwards we have at the club.”