Fox was delisted by the Swans after an injury-cursed 2025 season in which he failed to play an AFL game.
Originally from Burnie, Fox enjoyed a 105-game AFL career at Sydney as one of the club's many rookie-list success stories.
"I am looking forward to being back in Tasmania to help others grow and develop myself in this next chapter," Fox said in a statement.
"To be a part of this club from the first VFL bounce is a once-in-a-lifetime opportunity.
"My discussions with the club have been so positive. I understand and believe in the opportunity of this club to have a huge impact across Tasmania, and I cannot wait to be a part of that."
The 32-year-old featured in both the 2022 and 2024 grand finals, when he was one of few Swans to stand up in the shellackings.
Fox's recruitment follows that of fellow Tasmanian Jye Menzie, who this week became the Devils' first VFL signing after being delisted by Essendon.
Liam Jones, another delisted Tasmanian with AFL experience, is also on the Devils' radar.
Tasmania's list manager Todd Patterson described Fox as "almost exactly what you need from a VFL perspective".
"Given he is so mature, such a good communicator and able to play in various positions," Patterson said.
"To be able to add someone of Robbie's experience to our squad is a great sign of the belief in what we are building."
The Devils will field VFL and VFLW sides in 2026, ahead of their entry into the AFL and AFLW in 2028.
The league has made it clear Tasmania won't be the home of the 19th AFL team if it does not build a roofed stadium at Macquarie Point in Hobart.
That $1.13 billion project, which requires parliament's approval, is set to be voted on in November.
It has been a big week for the expansion club headed by former Richmond chief executive Brendon Gale.
The AFL finalised a stack of list concessions for the Devils, including the green light to spend $5 million above the salary cap to lure players.
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