"I always look forward to new challenges and experiences with a new team, and also moving my family for the first time outside of New Zealand," he said.
"Over the last couple of years, there seems to be a shift in the way the Rebels are playing, and there seems to be a lot of hard work; they're exciting times moving forward.
"I'm really looking forward to working with Tony McGahan, Zane Hilton and the Rebels' Rugby program, as well as playing alongside a squad of players who I've enjoyed coming up against, and really respected as opponents."
Rebels' Head Coach Tony McGahan said that the Club would benefit from Retallick's experience and skillset.
"Culum coming from a strong Rugby environment in New Zealand will bring a great deal of experience for us in the lock position," McGahan said.
"His set piece work will add to our depth and playing style, as we look to improve on the 2015 season. We look forward to Culum and his family moving to Melbourne in November to commence pre season training."