The 23-year-old was already contracted with the Sea Eagles until the end of 2020, but his new contract sees him sign on for a further two years.
Fonua-Blake has played 60 first-grade games in the NRL since making his debut for the Sea Eagles back in 2016.
He played for New Zealand at the 2017 World Cup but has most recently represented Tonga, where he has earned three caps.
On retaining Fonua-Blake, Manly’s coach Des Hasler said: “It’s a wonderful signing for our club.
“Addin can become one of the great Manly Warringah Sea Eagles front-rowers in its history.