A three-time premiership winner and NSW State of Origin representative, the hooker will turn 34 just after his new deal finishes at the end of 2026.
Koroisau joined from Penrith this year and has been the Tigers' most consistent player in a dire campaign that is trending towards a second-consecutive wooden spoon.
The captain's new contract is a major show of faith in the finals-starved Tigers and means he will help usher in a new era under Benji Marshall, who will replace Tim Sheens as coach in 2025.
"I'm grateful for the opportunity to further demonstrate my commitment to the club," Koroisau said.
"I'm excited for the present and the future, and I'm just so proud to be leading our team."
Koroisau's leadership has been vital for a Tigers side cruelled by injuries this season and currently relying heavily on young talents including Jahream Bula, Junior Tupou and Fonua Pole.
"He is a great leader, and he has done a wonderful job this season," coach Sheens said of Koroisau.
Koroisau's new contract comes after the Tigers announced on Wednesday night they had secured the promising brothers Latu and Samuela Fainu from Manly juniors on four-year deals.
With their hooker locked in, the Tigers' attention now shifts to securing a halves pairing to begin the 2024 season.
Long-term halfback Luke Brooks is preparing to join Manly, while first-choice five-eighth Adam Doueihi is likely to miss the majority of next year with his anterior cruciate ligament injury.
Former Canberra halfback Aidan Sezer, and Jack Cogger - Penrith's understudy for Nathan Cleary - have been floated as options.
8°C