New York announced the move, dealing for Baez, pitcher Trevor Williams and cash considerations while sending prospect Pete Crow-Armstrong to Chicago.
Baez has developed into one of MLB's most well-rounded shortstops since becoming a full-time player for the Cubs in 2016. He enjoyed a strong 2019 season during which he posted a .281/.316/.531 triple-slash line with 29 home runs across 138 appearances.
Although those are rock-solid numbers, they weren't quite as strong as his breakout 2018 campaign, which saw him finish with career-high totals in OPS (.881), homers (34) and stolen bases (21).
He did post a lackluster .599 OPS in 2020 as part of the coronavirus pandemic-shortened season, but the sample size was far smaller than his previous productive years.
Baez has compiled a .775 OPS with 22 home runs in 91 games so far during the 2021 season.
The 28-year-old Puerto Rico native is also a wizard in the field. He ranked eighth among all MLB players with 15 defensive runs saved during MLB's last full season in 2019, per FanGraphs.
Baez has spent his entire career in the Cubs organization since being selected with the ninth overall pick in the 2011 MLB draft, and last September, he stated his desire to keep it that way.
"I grew up here, and hopefully I stay here my whole career," he told reporters. "We'll see."
Chicago emerged as a seller ahead of this year's trade deadline as it fell to the fringe of playoff contention and faced an offseason with several potential free agents. Baez, who of those players scheduled to hit the open market, became part of the sell off despite his desire to remain a Cub.
The shortstop will slot in alongside Pete Alonso and Dominic Smith in the middle of the Mets' batting order following the blockbuster deal. He'll likely start out at shortstop but could switch positions once Francisco Lindor returns from the injured list.