The deal is worth $1.5 million, plus $600,000 in performance bonuses, according to Boesch's agent, Scott Boras. Boesch was released by the Detroit Tigers on Wednesday after three big-league seasons with the team.
Yankees general manager Brian Cashman did not immediately return a request for comment on the move.
Boesch could be part of a left-field platoon with the right-handed hitting Ben Francisco, who was signed earlier this week after he requested his release from the Cleveland Indians. Usual left fielder Brett Gardner will fill in in center for Curtis Granderson, who suffered a broken right arm after being hit by a pitch on Feb. 24. That injury will keep him out of the lineup until early May.
This spring, the Yankees had been auditioning veterans Juan Rivera and Matt Diaz, as well as rookies Zoilo Almonte, Melky Mesa and Ronnier Mustelier, to fill in at one of the corners until Granderson returns. Mustelier was injured in Friday's game against the Miami Marlins.
Boesch, a left-handed hitter -- as are the two remaining starters, Gardner and Ichiro Suzuki -- batted .240 with 12 home runs and 54 RBIs last season. His best year was 2011, when as a second-year player he hit .283 with 16 homers and 54 RBIs.