The Mets announced in a statement that they have reached an agreement with Bay to terminate his contract two years early, granting him unconditional free agency.
Financial terms were not disclosed.
"I still feel I have plenty to give to this game and that I can play baseball at a high level. But after serious consideration, both sides agree that we would benefit from a fresh start," Bay said in a team-issued statement. "I'm grateful we were able to reach an agreement to allow that to happen."
Mets general manager Sandy Alderson, in attendance at the GM meetings, was not immediately available for comment. In the team's statement, he said: "Jason has a tremendous work ethic. There was never any question about it. Unfortunately, the results weren't there and we are in a results-oriented business. We thank Jason for his efforts and wish him well."
Bay signed a four-year, $66 million contract in January 2010 that was negotiated by Omar Minaya, Alderson's predecessor, but Bay's time as a Met was marred by injuries and a mystifying inability to hit for power after four seasons of having hit at least 30 home runs for the Pittsburgh Pirates and Boston Red Sox.
In his three years as a Met, Bay hit a total of 26 home runs and drove in 124 runs. A career .269 hitter, he batted just .234 as a Met.
Bay, 34, suffered a concussion running into the wall in his first season with the team and appeared in only 95 games. He also suffered a rib injury that limited him to 123 games in 2011, and a broken rib that kept him out of all but 70 games in 2012.
Bay's contract, which carried an option for a fifth year, called for him to be paid $16 million in the coming season, with either a club option for $17 million for 2014 or a $3 million buyout. He also had a full no-trade clause. The 2014 club option would have vested with 600 plate appearances in 2013.
"I'm excited to keep playing and have no intention of just walking away," Bay said. "I enjoyed my time in New York. I have no regrets in signing with the Mets, other than that I wasn't able to play to the level that the team, the fans and I all expected and that we weren't able to win more games. I move on with nothing but an appreciation for the organization and its fans and best wishes to all my teammates there."