The Tigers announced on Monday the 19-year-old, among the top talents of his generation, would not be at the joint venture after his contract expired at the end of the 2026 season.
Campbelltown product Galvin rejected what the club called "the largest offer for a junior in the history of the club" - reportedly worth around $5 million across five seasons - and will be free to negotiate with rival clubs from November 1.
The Tigers will not entertain an early release for Galvin, whose future had already been subject to speculation before a ball was 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 Galvin will not be up for grabs as the NRL undergoes a halves merry-go-round for 2026.
Parramatta and Manly are both hunting an elite playmaker for next season given the impending departures of Dylan Brown and Daly Cherry-Evans but would need to wait another year to have Galvin on their books.
"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 set 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.
Galvin played junior football for the Eels before being cut and landing at the Tigers to help feeder club Wests win the Harold Matthews Cup in 2022.
He is also managed by Isaac Moses, who also handles Eels half Mitch Moses.
But for Parramatta, making a play for Galvin would mean finding a stop-gap to play next to halfback Moses in 2026.
Galvin's manager also has strong ties to the Sea Eagles, counting coach Anthony Seibold, five-eighth Luke Brooks and winger Tommy Talau among his clients there.
Manly are currently in the hunt for a playmaker to replace Cherry-Evans and have been linked with Canberra veteran Jamal Fogarty.
Canterbury general manager of football and broadcast pundit Phil Gould has previously spoken highly of Galvin, whom he last year rated as the best teenage talent he had ever seen.
The Bulldogs recently ruled out making a play for Cherry-Evans for 2026 on the grounds they backed their current first-choice playmakers Matt Burton and Toby Sexton.
But a 19-year-old with a bright future ahead could be a different proposition.
Bulldogs prop Max King laughed off speculation Galvin could join the Bulldogs from 2027 when quizzed on Monday.
"It's out of my jurisdiction to be making those calls, otherwise I'd just be signing myself up for a million bucks," he joked.
"Our depth has been a massive part of us and I just love where we're going as a club."
