Bell confirmed the move on social media by posting a photo of himself in a Jets jersey.
"I'm back in the green baby, let's get it," Bell wrote on Twitter.
Bell, 27, had 1,291 yards and nine touchdowns on a league-high 321 carries in 15 starts during the 2017 season. He also had a league-high 406 touches for 1,946 yards from scrimmage while being named an All-Pro for a second time in his last full season.
He sat out the Steelers' 2018 season after refusing to sign his franchise tag tender. The three-time Pro Bowl selection had 1,884 yards from scrimmage and nine touchdowns in 12 starts during the 2016 season. Bell had a career-high 2,215 yards from scrimmage and 11 scores during his first All-Pro season in 2014.