The 27-year-old Tonga international joined Trinity from NRL side Canberra Raiders in 2015 and has scored 15 tries in 48 appearances.
Tupou has played both centre and wing for Wakefield, who travel to Castleford in the Super 8s on Thursday.
"I'm very happy to have signed a new deal, myself and my partner are very happy here in Wakefield," Tupou said.
Head coach Chris Chester added: "I am pleased that 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."