Coach Brian McDermott knows his two stalwart front-rows will not go on forever with both likely to retire at the end of next season if not before.
Cuthbertson, 29, will, therefore, join the Headingley club at the end of this campaign on a four-year contract.
He comes highly recommended by Danny Buderus, the former Australia captain who spent three years at Leeds before returning to Newcastle in 2011 where he is now a coach.
Cuthbertson, whose family are from Warrington, started at Manly, featuring in the 2007 Grand Final before facing Leeds in the World Club Challenge two years later. Following a spell at Cronulla, he moved to St George, where he first worked under the great Wayne Bennett, the coach who also took him to Newcastle.
“As an experienced NRL professional, not only will Adam add quality to our group but he will also help our younger players develop and realise their full potential with his knowledge,” said McDermott. “Given the state of the game in Australia and demand for front-rowers over there, this is a massive boost for the Rhinos and a big decision for Adam.
“However, he’s a passion to play in our comp’ and for Leeds.”
Leeds chief executive Gary Hetherington revealed the West Yorkshire club tried signing the player three years ago but he opted to follow Bennett to Newcastle instead. He added: “At 29, Adam is at the peak of his powers as a prop and he has agreed a long-term contract with us, showing his commitment to coming to Leeds and our competition.
“Adam will effectively replace Ben Jones-Bishop in our senior 25-man squad which means all our players are now contracted for next season.”