Kaufusi, 28, joins on a two-year deal following his release by the capital club, and follows Chris Bailey to the John Smith’s Stadium.
Giants coach Paul Anderson said: “Antonio brings a wealth of experience to the Giants, his pedigree is unbelievable. He’s played in a NRL Grand Final, for Australia and in the State of Origin and there is no higher level of Rugby League in the world than State of Origin.
“We’ve never replaced Stuart (Fielden) or Luke O’Donnell and along with Chris (Bailey) who we announced earlier in the week, he’ll certainly add depth to our squad.
“When we spoke I told him I want to see the form that made him a State of Origin player and that definitely sparked something in him. He had a lot of options and it’s a credit to us and where we are at that he saw us as an attractive proposition.”
Kaufusi played for Melbourne, North Queensland and Newcastle in the NRL before moving to London on a three-year deal ahead of the 2012 season.