Galea, 33, has made more than 100 appearances during the past four and a half seasons, and had hoped to secure a contract for next year, but has been unable to agree terms with the club.
He said: “I am extremely disappointed that the club and I have not been able to reach an agreement for the 2013 season. I still feel a huge desire to play rugby league now and beyond the 2012 season, making me extremely reluctant to hang up the boots.
“I have thoroughly enjoyed the past five seasons at Hull KR and will be sad to leave. I would like to thank my team mates, the club and the supporters for making my time at Hull KR the fantastic experience it has been. I will continue to wear the red and white jersey with pride and give my best until the final whistle blows.”
Robins’ chief executive Mike Smith said: “In the four years that I’ve been here, Ben has been a pleasure to deal with. He’s a consummate professional, both on and off the pitch, and has often provided the link between the players and the club, even before he was made captain at the start of this year.
“He’s also an exemplary role model to the younger players we have at Hull Kingston Rovers and has played a big part in helping to establish the club in Super League during the past five years. We’d liked to have kept Ben here for another season but unfortunately an agreement couldn’t be reached, hence the reason he will be moving on at the end of the year.”