Barnes will make $1.65 million in the first year, including a signing bonus. His second- and third-year salaries are $1.2 million, but they can increase to $2 million with escalators, a source said.
Barnes, who visited with the Jets last week, made the announcement on his Twitter account, saying: "Green and White, it is." He thanked the team's braintrust, adding, "To the fans, I won't let you down."
He later backtracked as the two sides worked out the final details of the contract, which is worth $4 million. By late afternoon, it was a done deal.
Barnes will be reunited with Rex Ryan, his defensive coordinator with the Baltimore Ravens in 2007 and 2008. Coordinator Dennis Thurman also is a former Ravens assistant who has worked with Barnes. The Jets tried to sign him in the past.
Even though he has been a pass-rushing specialist his entire career, Barnes, 28, will have the opportunity to start.
The roster is bereft of outside linebackers after the recent release of Calvin Pace, who started for five seasons. The other starter, free agent Bryan Thomas, won't be re-signed. Barnes' competition is Garrett McIntyre and Ricky Sapp.
This will be Barnes' fourth team in seven years. He has 23.5 career sacks, including 11 in 2011 for the Chargers. Curiously, his production took a big dip last season, as he managed only three sacks in 11 games.
The Jets' sack production has declined in each of the four seasons under Ryan, and they need a pass-rushing presence on the edge.
Barnes once sacked Joe Flacco four times in a game. He also had a two-sack game against Tom Brady, which no doubt appealed to Ryan.
The Jets needed to do something to help their eighth-ranked defense, which lost three starters in free agency -- tackle Mike DeVito and safeties LaRon Landry and Yeremiah Bell.