The announcement confirms earlier reports that Alderson and the Mets were working on an extension.
Alderson was hired as the general manager at the conclusion of the 2010 season, replacing Omar Minaya.
The Mets won an average of 75 games in Alderson's first three seasons. They are 76-80 this season, with six games left to play.
Alderson hired Terry Collins to be the team's manager when he took over. The team also announced Collins will return in 2015.
- Dan Gartland