"I've been around the Vodafone Warriors for a few years now and I've got a lot to thank the club for.
"I've enjoyed having the chance to play in the NRL regularly but I also know I have to work at my game and keep improving to hold on to my place."
Warriors head coach Brian McClennan said Tupou's new deal was well-deserved.
"Bill's one of our most improved and reliable players," he said.
"He has developed into a consistent first-grade player and, like so many in our NRL squad, he's an example of what local players can achieve by coming through our development system."
Tupou is, in fact, one of 18 players in the club's NRL squad to come through the Junior Warriors. While he was ruled ineligible for the 2010 NYC grand final, he was a major contributor to the premiership-winning campaign finishing his three years in the competition with 37 tries in just 49 games.
Confirmation of his contract extension caps a good week for the former Kelston Boys' High School pupil.
In last week's Anzac Day NRL clash against the Melbourne Storm, Tupou showed excellent finishing skills to score two tries, his second double of the season.
The team's top try-scorer so far with five, his performance earned him the players' player of the day award.
Tupou will make his 38th NRL appearance when the Warriors face Brisbane in Saturday night's ninth-round encounter at Mount Smart Stadium.