New York agreed to the deal Dec. 13 during the winter meetings, and the 36-year-old took a physical on Tuesday.
His addition, following last month's $324 million, nine-year contract with pitcher Gerrit Cole, raised the Yankees' projected luxury tax payroll to about $248 million — the threshold where the highest luxury tax rate starts.
Gardner gets a $2 million signing bonus payable Jan. 30 and an $8 million salary for next season. The Yankees have a $10 million option for 2021 with a $2.5 million buyout.
New York opened a roster spot by designating left-hander Stephen Tarpley for assignment.
Gardner earned $7.5 million last season plus a $2 million buyout after New York declined his $12.5 million option for 2019 under his previous contract. He hit .251 and set career highs with 28 homers and 74 RBIs, a rare left-handed bat in a Yankees lineup dominated by right-handed hitters.
Gardner is the senior member of the Yankees, having spent his entire 12-year big league career in the Bronx. He has a .260 average, 124 homers and 524 RBIs.
He is expected to see time in center field during the first half of the season while Aaron Hicks recovers from offseason Tommy John surgery, then shift back to left when Hicks returns.