The former Leeds, Hull and Bradford forward is an ex-England international with over 250 first-team appearances in the top flight.
Having initially signed for the club earlier in the season, Scruton has committed to the Robins despite the drop to the Kingstone Press Championship.
“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,” he said.
“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.
Head of rugby Jamie Peacock added: “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.”