The 24-year-old, who came through the ranks at Leeds Rhinos, is the second player to join the Giants ahead of the 2018 season, with former Salford Red Devils prop Adam Walne having already completed his move to the John Smith's Stadium.
Roche, who also has two caps at international level with Ireland, admits he is looking forward to making the step up to Super League level and he is hoping he can develop as a player during his spell with the Giants.
"I'm definitely excited. It's a club that as soon as they gave me a call and asked me to join I jumped at the chance," Roche told the club's official website.
"Just being in the changing room and around the stadium, with all due to respect to the Championship clubs, this is a different world and I'm really looking forward to the professionalism at this club and to make myself a better player in every opportunity I get."
Giants coach Rick Stone has also welcomed the arrival of Roche, as he feels the forward's versatility will make him an integral member of the squad.
"He's a young lad we feel deserves an opportunity in full-time Super League," said Stone.
"He's a forward that can operate in a number of roles and offer greater depth to our squad and we look forward to seeing how he progresses in 2018 pre-season training."