The 6ft 5ins front- rower has been with the Titans since 2015 and previously played in the lower grades at New Zealand Warriors.
Peteru was born in Auckland and is of Samoan and Cook Islands descent.
He played his junior rugby at Glenora Bears and made a try scoring debut for Titans in 2015.
Peteru has played 15 times for the Titans this season in the NRL, a career high in his three seasons on the Gold Coast.
“I am really looking forward to joining the Rhinos,” Peteru said.
“I see it as a fresh challenge for me and I am excited about the opportunity to come on board with the team.
“We have been talking for a while, but it has speeded up over the last few weeks.
“My family and I are looking forward to coming to Leeds and for me personally playing in a new competition is something that inspires me.
“Having watched Leeds I know they have a winning culture and that is something I want to be part of, but most of all I am coming for the challenge.”
Peteru, who will link up with Rhinos for pre-season training, revealed he has spoken to former Rhinos prop Kylie Leuluai about making the move to Leeds.
He added: “I want to come to England and take my game to the next level. I believe I can do that with Leeds with a successful team and a successful coach.
“I have known Kylie Leuluai for a number of years. I watched him when I was growing up in New Zealand and followed his career when he was at Leeds.
“Talking to him put my mind at ease when I was looking to come over for a new challenge. Brian McDermott [Rhinos’ coach] and I have had a couple of conversations and he has been really positive about what I can do.
“He wants me to push to become a starting forward eventually and that is something I want to do consistently.”
McDermott reckons Peteru has the attributes to be a hit in Super League. He said: “Nathaniel is someone we have been keeping an eye on for a while and the opportunity arose to bring him over for next season.
“He is an impressive individual who spoke passionately to us about his commitment to the Rhinos and what he wants to achieve in his own game and with the Rhinos.
“Moving your family to the other side of the world is not something anyone takes lightly and it is a measure of Nathaniel’s desire to be successful with the Rhinos that he is ready to come over and be part of our club.”
Rhinos chief executive Gary Hetherington described Peteru as an “outstanding signing”.
He said: “I’m sure Nathaniel will prove to be a big success.
“He’s a big man with outstanding ball-handling skills and his style is ideally suited to Super League and Leeds Rhinos.
“Nathaniel is hoping to be selected for the Samoan team in the forthcoming World Cup, having shown himself to be a very good player in the NRL and his best years are ahead of him.
“His signing is another key building block in the foundation of the Leeds Rhinos team, which will continue to evolve over the next few years.”