The Samoan forward will leave the Knights to join the Super League outfit after making 74 appearances in the NRL for Canterbury, Wests, Brisbane, New Zealand and Newcastle.
The 29-year-old will also represent Samoa at the inaugural World Cup Nines tournament in Sydney this week.
“We were looking to add some size and aggression to our pack and we felt James was the best person to fill that role,” Giants coach Simon Woolford told Sky Sports.
“James had a number of options including some top Super League clubs, so we’re thankful to James and his management for making the choice to come to Huddersfield and we feel this is a major coup for the club.
“We feel it’s a very significant signing for the club moving forward in our quest to become a top-five Super League team.”
The Sydney-born prop says he held discussions with a number of teammates before selecting Huddersfield, with the Giants finishing just two points from the relegated London Broncos in 2019.
“I spoke to guys that I’ve played with, like Suaia Matagi and Ukuma Ta’ai and they told me about the talent in the squad and how well the team should have done last year,” Gavet said.
“They said that the position on the ladder didn’t represent the potential the team had and I have always rated them and their honesty.
“They are people I know and trust. I hope I can strengthen them and help them fulfill their potential. From what I’ve heard, they are heading in the right direction.
“I hope I can be the piece that fits perfectly to complete the puzzle.”