Rated among the brightest stars of his generation, the 19-year-old has rejected what the Tigers called "the largest offer for a junior in the history of the club" to test the open market in November.
Reports have indicated the offer was worth around $5 million across five seasons, marking a big pay rise from Galvin's estimated $350,000 salary for next season.
The Tigers will not entertain an early release for the Campbelltown product, whose future had been subject to speculation before a ball had been kicked in 2025.
Galvin's camp unsuccessfully agitated for an early exit from the club during a stellar 2024 rookie season but have not made the same request this time.
It means he will not be up for grabs as the NRL undergoes a halves merry-go-round for 2026, with Parramatta and Manly both on the lookout for elite halves following the impending departures of Dylan Brown and Daly Cherry-Evans.
"We would like to announce that Lachlan Galvin will not be with the club beyond the 2026 season," the Tigers said in a statement.
"Despite the club having the largest contract offer for a junior in the history of the club on the table, Lachlan and his management have decided his future lies elsewhere and were not willing to review the offer.
"Obviously, there will be a lot of speculation around this release, but we will make no further comment.
"The club is focused on winning as many games as possible during Lachlan's tenure and beyond. The club is disappointed, but we move on."
The news looms as a crushing blow for a Tigers side finally appearing to find its feet after three consecutive seasons finishing on the bottom of the ladder.
After years struggling for direction from their halves, the Tigers have forged an impressive 3-3 start to the year thanks in no small part to Galvin's chemistry with new halfback Jarome Luai.
There is expected to be significant rival interest in Galvin, who would likely have won the Dally M Rookie of the Year award in 2024 but for a two-game suspension.
Parramatta are expected to be keen on the teen sensation given they will lose five-eighth Brown to Newcastle for 2026 and are yet to lock down an elite replacement.
Galvin played junior football for the Eels earlier in his teen years before being cut loose and landing at the Tigers to help feeder club Wests win the Harold Matthews Cup title in 2022.
Galvin is also managed by Isaac Moses, who counts Eels half Mitch Moses among his clients
But for Parramatta, making a play for Galvin would mean finding a stop-gap to play next to halfback Moses in 2026.
Manly, Canberra and Penrith are among other NRL clubs facing uncertainty around the future of their halves for 2026, but would also need to find contingencies for next year if they pursued Galvin.
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