Green, who was due to come out of contract at the end of next season, was considered one of the Devils' prime targets ahead of entering the AFL in 2028.
But the tough midfielder, who missed all of last season with an ACL tear, has knocked back big money from Tasmania and instead added two more years to his deal at GWS.
Green's signature is huge after an off-season where the Giants lost their captain and biggest name Toby Greene to Geelong.
The 25-year-old, who won the Giants' best and fairest in 2025 and finished fifth in the Brownlow Medal in 2024, appears almost certain to replace Greene as captain.
Former academy prospect Green was drafted at pick No.10 in the 2019 draft and has since played 115 games and kicked 49 goals since his debut in 2020.
"Tom is a very important leader of our footy club and ensuring he's a Giant for the next three years is a fantastic result," outgoing GWS chief executive Dave Matthews said in a statement.
"Tom has been a Giant since joining our Academy in Canberra and since then he's personified exactly what it means to be a Giant, both on and off the field and to have him remain a Giant amid such rival interest is a profound moment for us as a club.
"Tom embodies everything that the Giants stand for and to have him recommit to the club is really significant as we enter what is a really exciting time for the club," added Matthews.
"While his football speaks for itself as one of the best players in the competition, he's also an incredible leader and a terrific person who set the standard for his teammates around him.
"Tom helps form a really exciting core of leaders at our club and his decision to stay at the Giants is going to be an immensely popular one across his teammates and the whole club."
Elsewhere, Gold Coast have delisted Jamarra Ugle-Hagan but committed to redrafting the key forward.
Former Western Bulldogs No.1 draft pick Ugle-Hagan was handed a career lifeline by the Suns last season but played just three games.
The Suns have also cut injury-ravaged tall Elliott Himmelberg but, like Ugle-Hagan, will pick up the former Adelaide forward at next month's draft.
St Kilda delisted Dan Butler and Ryan Byrnes and have committed to picking up the pair in the rookie draft.
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