Fusitu'a is now set to become the eighth Warriors player to clock up a decade of service.
The 23-year-old wing, who debuted as a teenager in 2014, has scored 47 tries in 75 games for the Warriors.
He is currently fourth on the NRL try scoring lists with 15 tries in 18 matches this season.
Coach Stephen Kearney said it had been a priority to retain the powerfully built player, who has played in the centres and at fullback for the club before settling on the right flank.
"There's no question he has made tremendous progress, especially over the last two seasons," he said.
"He provides wonderful value for us in all respects.
"He's a player the club has put a lot of work into to develop into a high-quality footballer and he is repaying the faith we have always had in him," Kearney said.
Fusitu'a said he was excited to secure his future with the Warriors.
"I'm thankful to the club for having faith in me."
"I grew up always wanting to be a part of the Vodafone Warriors and I'm committed to seeing this club succeed and doing something special here," he said.
"This is where I want to be."
Fusitu'a played two tests for New Zealand in 2016 before representing Tonga at last year's world cup, scoring a hat-trick against his former side.