The Mets on Thursday extended Lagares' contract through 2019, with an option for the following year.
The deal covers all of Lagares' arbitration years and guarantees him $23 million from 2016 to '19. It includes a $9.5 million team option for 2020, which would be the first season that Lagares otherwise would be eligible for free agency.
Lagares, 26, hit .281 with four homers and 47 RBIs in 416 at-bats in 2014. According to ESPN Stats & Information, he led all major league center fielders with 28 defensive runs saved in 2014. That total nearly doubled the center fielders with the next-highest totals, Ender Inciarte of the Arizona Diamondbacks and Leonys Martin of the Texas Rangers (15 apiece).
In November, Lagares became the third Mets outfielder to win a Gold Glove, joining Carlos Beltran and Tommie Agee.
Alderson predicted Lagares would continue to improve.
"We think there's enough trajectory, but [there] doesn't have to be in order for us to be happy with this deal," Mets general manager Sandy Alderson said. "... Baseball rewards exceptional performance in whatever area -- whether it's power, hitting for average, great defense. But he's shown that he can play great defense and still carry a bat sufficiently to stay in the lineup. From that standpoint, he's moving toward becoming a complete player."
Lagares was in New York on Thursday for a physical.
The Mets last did a long-term extension covering arbitration years and initial free-agency years with left-hander Jonathon Niese on the eve of the 2012 season.
Alderson acknowledged the Mets also are currently talking to first baseman Lucas Duda's representatives about a potential long-term deal, although it previously has been acknowledged that the sides would drop talks if nothing is reached by Opening Day.
"A deal has to be attractive to both sides," Alderson said. "If we check those boxes, then maybe something happens with Lucas."
ESPN's Jim Bowden contributed to this report.