De Aza will get a one-year deal worth $5.75 million, according to a source.
The deal also contains an additional $1.25 million in performance bonuses, The Associated Press reported, citing a person familiar with the negotiations.
De Aza, 31, primarily would serve as a lefty-hitting complement to Juan Lagares in center field. He joins Lagares as well as lefty-hitting corner outfielders Michael Conforto and Curtis Granderson with the reigning National League pennant winners.
The Mets remain in the market for a righty-hitting backup outfielder to offset the retirement of Michael Cuddyer.