De Aza can earn an additional $1.25 million in performance bonuses based on plate appearances under Wednesday's deal: $250,000 for 400 and each additional 50 through 600.
The 31-year-old bats left-handed and could platoon in center field with right-handed-hitting Juan Lagares.
De Aza batted .262 this year with seven homers - all off right-handers -and 35 RBIs in 365 plate appearances for Baltimore, Boston and San Francisco. Lagares hit .253 against right-handers, 20 points under his average against lefties.
New York was seeking an outfielder in place of Yoenis Cespedes, who became a free agent after helping the Mets reach the World Series for the first time since 2000.
De Aza is represented by the joint venture between singer Marc Anthony and agents Barry Praver and Scott Shapiro.