The 27-year-old joined Trinity in July, 2015, from NRL side Canberra Raiders, initially on a deal until the end of that season.
He later signed a two-year contract extension and has become a key player in coach Chris Chester’s side, scoring 15 tries in 45 appearances.
Tupou said: “I am very happy to have signed a new deal. Myself and my partner are very happy here in Wakefield.
“I am excited to stay here at the club. It has been a great two years, the boys and coaching staff are always in high spirits and are there for me so I am looking forward to the next three years.”
Chester said: “I am pleased we have been able to secure the services of Bill Tupou for a further three years.
“He has had an outstanding season adding some great depth to the squad. I look forward to see him grow as a player and working alongside him in the future.”