NFL Network first reported the deal.
In a span of several hours overnight, the Jets reshaped their linebacker corps for new defensive coordinator Gregg Williams, adding Mosley and Anthony Barr, who have eight Pro Bowl appearances between them. The total cost will be approximately $32 million per year.
The Jets envision Mosley, 26, as an inside linebacker in their 3-4 scheme and the leader of the front seven. They now have five starting-caliber linebackers, with Mosley, Avery Williamson and Darron Lee inside and Barr and Jordan Jenkins outside. Williamson's $6 million salary is fully guaranteed, so he likely will remain as Mosley's inside partner.
Mosley was the leading tackler for the NFL's top-ranked defense and was the Baltimore Ravens' most high-profile free agent this offseason. He is one of two players, along with Carolina's Luke Kuechly, to record at least 500 tackles, eight sacks and eight interceptions since 2014.
A first-round pick (17th overall) in 2014, Mosley has gone to the Pro Bowl in four of his five NFL seasons, which puts him in select company. Seven of the 11 linebackers who were named to Pro Bowls at least four times in five seasons are in the Hall of Fame. Last year, Hall of Famer Ray Lewis called Mosley the best middle linebacker in the game.
This marks the first time in the Ravens' 23-year history that they have failed to keep a multiple Pro Bowl first-round pick past his rookie deal. Offensive tackle Jonathan Ogden, Lewis, outside linebacker Peter Boulware, cornerback Chris McAlister, tight end Todd Heap, safety Ed Reed, outside linebacker Terrell Suggs and defensive tackle Haloti Ngata all signed second contracts with Baltimore.
In a span of a week, the NFL's top-ranked defense has now lost its two signal-callers, Mosley and safety Eric Weddle; its most tenured player, Suggs; and linebacker Za'Darius Smith. Mosley, Weddle and Suggs have combined for 460 NFL starts and 17 Pro Bowls.
The biggest knock on Mosley has been his pass coverage, but his interception of Baker Mayfield in the final regular-season game clinched Baltimore's first playoff berth in four years. Mosley also posted career lows in passing yards allowed (408), yards per reception (9.3) and yards after the catch (190), according to Pro Football Focus.
The Ravens and Mosley both expressed optimism he would remain with the team. Baltimore, however, chose not to use a $15 million franchise tag, allowing Mosley to become a free agent.
With Mosley gone, the Ravens could replace him with Kenny Young, a fourth-round pick from a year ago, or a veteran free agent.
Mosley's 574 career tackles rank fifth in Ravens history.
Lee, a former first-round pick, faces an uncertain future. He hasn't met expectations over three years and finished last season with a four-game, substance abuse suspension. He counts only $3.3 million on the cap in the final year of his rookie contract, so he could be traded or released. His $1.8 million salary no longer is guaranteed because the guarantee was voided by the suspension.
One source cautioned that Lee could remain on the Jets roster in a backup role, with Williams finding creative ways to use him.
ESPN's Jamison Hensley and Rich Cimini contributed to this report.