The Jaguars did not reveal the terms of the deal, but NFL Network Insider Ian Rapoport reported it was for two years and worth $10 million.
"I've been through ups and downs in this league; I've seen a lot of guys go and a lot of guys come," Seferian-Jenkins said. "It's a big carousel. I feel very fortunate that I have this opportunity."
Seferian-Jenkins is coming off the best season of his four-year career, hauling in a career-high 50 receptions for 357 yards and three touchdowns in 13 games for the New York Jets.
A second-round draft pick of Tampa Bay in 2014, Seferian-Jenkins spent two-plus uninspiring seasons with the Buccaneers before he was waived early in 2016. He had 55 catches in 25 games with Tampa Bay.
Seferian-Jenkins, who reportedly turned down a two-year, $8 million contract from the Jets, becomes the fourth offensive player and second tight end brought in by Jacksonville during free agency.
Seferian-Jenkins said he likes the direction of the team under coach Doug Marrone.
"I love Coach Marrone," he said. "He's a cool dude. He's from the Bronx. I kind of vibe with him. (Tight ends) Coach (Ron) Middleton is a great tight ends coach and Coach (Nate) Hackett is a phenomenal OC. They have a great quarterback in Blake Bortles. They have a lot of pieces. ...
"There are pieces all over the place. The offense is really coming together right now. I had to jump on the opportunity. This opportunity doesn't come around a lot."