Bay, a three-time all-star, came to the Mets in 2010 after clubbing an average of 31 home runs per year from 2005-09 with the Pirates and Red Sox. He managed just a .234 batting average with 26 home runs over 288 games in New York after signing a four-year, $66 million deal.
Mets Chief Operating Officer Jeff Wilpon said in a statement the club and Bay, 34, have agreed to "part ways."
"Jason is a great teammate, hard worker, stand-up guy, and true gentleman," Wilpon said. "Like Jason, we had planned for the kind of production here that he enjoyed in Boston and Pittsburgh, where he established himself as one of the game's top players. We wish Jason and his family success and happiness in the future."
"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," Bay said in a statement.