The deal includes a $6M conditional option for the 2017 season.
Aoki, 33, was limited to 93 games with the San Francisco Giants in 2015, batting .287 with five home runs and 26 RBIs before a small fracture in his right leg and a concussion derailed the second half of his season.
The Giants declined his $5.5 million option after the season.
Aoki suffered the concussion on Aug. 9 when he was hit in the head by a pitch against the Cubs. He returned to the lineup three games later but played only five innings before running into a wall to make a catch. After complaining of nausea and an inability to focus, he again was put on the DL.
He missed 28 games with the leg injury.
Aoki came to the majors from Japan, joining the Milwaukee Brewers in 2012. In four seasons with the Brewers, Giants and Kansas City Royals, the left-handed hitting outfielder has a .287 batting average with 91 doubles, 81 stolen bases and 156 RBIs.