Thomas Fletcher made seven first-grade appearances for South Sydney across the past two seasons before moving to Auckland.
The 22-year-old back-rower has joined the One New Zealand Warriors on a three-year contract.
He played four NRL games in 2025 and three in 2026, along with 38 appearances in the New South Wales Cup.
Warriors general manager of recruitment, pathways and development Andrew McFadden said, "Thomas is a quality back rower who now has the chance to build his career with us."
McFadden noted the departures of Kayliss Fatialofa, Marata Niukore and Morgan Gannon: "We've had some back rowers who have moved on in Kayliss Fatialofa, Marata Niukore and Morgan Gannon."
He added, "Thomas boosts the resources there and has the opportunity to create a future here in the same way Jackson Ford has."