The 27-year-old Fusitu'a, who was the Warriors' longest-serving player, had two years left on his contract with the Auckland club and it is thought the Warriors will pay a proportion of his Leeds salary.
Fusitu'a, whose hat-trick famously helped Tonga beat New Zealand in the group stages of the 2017 World Cup, scored 61 tries in 108 appearances for the Warriors.
But he has played just 28 times in the last three seasons due to injury and returning home from Australia early in 2021, due to the border restrictions enforced by the global pandemic.
