The 28-year-old has signed a two-year deal with the club, and will arrive in the UK from New Zealand in November to join preseason.
“After 10 years at the Vodafone Warriors, I can’t wait for the new challenge of playing English Super League,” said Rapira.
“I decided to sign up with the Giants because I’ve heard positive things about the club and they have shown a lot of enthusiasm in getting me over there.
“I’m really grateful for this opportunity and I look forward to working with Paul Anderson and the boys.
“The thought of moving to the other side of the world with our two daughters is a bit daunting but our friends and family have been supportive throughout this process and we are excited to experience a new country and culture.”
Rapira has also taken advice about life in the UK from the Warriors’ resident Englishman, who is returning to Super League himself in 2016.
“We’ve had lots of advice from Sam Tomkins and his partner Charlotte,” said Rapira.
“It’s nice to know that we’ll have a few English friends over there in addition to our Kiwi friends.”