Financial terms were not disclosed.
Singleton, 30, who likely will be Oakland's centerfielder, batted .262 with nine home runs, 50 RBI, and 20 stolen bases last season for the Baltimore Orioles, who did not tender him a contract last week.
Singleton, who broke into the majors with the Chicago White Sox in 1999, has a .278 career average with 44 homers, 229 RBI and 74 steals in 556 games.
He has spent the majority of his playing time in center, and could replace Terrence Long, who is expected to be shifted to leftfield next season.
Swim Week Miami Beach 2014 [PHOTOS]