The strapping left winger put pen to paper just three weeks after right winger David Fusitu'a signed on until 2023.
Captain and fullback Roger Tuivasa-Sheck was already on a contract through to 2021, meaning the Warriors can build around a back three described as the best in the competition by Newcastle playmaker Mitchell Pearce.
It completes a memorable period for Maumalo, who has played a part in the club's surge to the finals and whose first child was born just a few days ago.
The 24-year-old's fourth season with the Warriors has been his best, currently ranked 12th in the NRL for most runs (339) and 10th for most metres (3283m).
Adding footwork to match his size has helped Maumalo develop into an invaluable asset, said coach Stephen Kearney.
"He has shown tremendous progress this season with his consistency and attitude.
"Together with David he gives us so much value at both ends of the field and has plenty of improvement in him."
Maumalo has played four Tests for Samoa but made his New Zealand debut in the loss to England in Denver in June.
"I feel a lot better about playing in the NRL now," Maumalo said.
"I'm more relaxed and I am enjoying my footy. That's the most important thing."