New York sent Cleveland outfielder Matt Lawton, outfield prospect Alex Escobar, pitcher Jerrod Riggan and two players to be named in exchange for Alomar and two players to be named, a baseball official familiar with the trade said on the condition he not be identified.
The trade, the first big deal of the winter meetings, was first reported by Newsday on its Web site this morning.
The deal between Mets general manager Steve Phillips and new Cleveland GM Mark Shapiro was completed between midnight and 12:30 a.m., another baseball official said, also on the condition of anonymity.
The Mets and Indians called a news conference for 11 a.m. but did not announce the subject.
It was the second major move in four days for the Mets, who dealt third baseman Robin Ventura to the Yankees last Friday for outfielder David Justice. It means New York most likely will move Edgardo Alfonso from second base to third next season.
After winning the NL pennant in 2000, the Mets failed to make the playoffs this year, finishing with the fewest runs and lowest batting average in the major leagues and the second-fewest homers in the NL.
The 33-year-old Alomar is a 12-time All-Star who hit a team-high .336 this year with 20 homers, 100 RBIs and 30 steals.