The Roosters reportedly kept news of Salesi Foketi's deal under wraps until after Sunday's grand-final win, their first premiership in seven years.
News Corp reports Foketi has agreed to a three-year extension, taking his contract through to the end of 2030.
He was contracted through next year, but the Roosters wanted him secured before the November 1 deadline.
The deal was understood to be done before then, though it may have been agreed earlier.
At 22, Foketi has become a regular second-row starter under Trent Robinson after filling in for Angus Crichton.
Crichton is leaving for rugby union, giving Foketi a long-term place on the edge.
Foketi has played 45 NRL games since debuting last year, including 26 appearances this season; he missed two of the Roosters' 28 matches, both early in the year.
Second-rower salaries have risen sharply, and Foketi would have attracted interest.