Davis hit .235 with 10 homers and 46 RBIs in 336 at-bats with Pittsburgh after the April 18 trade for minor league right-hander Zack Thornton as well as left-hander Blake Taylor, who subsequently arrived as the player to be named.
Davis was a probable non-tender anyway by the Dec. 2 deadline, since he earned $3.5 million in 2014.
Pedro Alvarez will serve as Pittsburgh's first baseman. He also bats left-handed and primarily played third base this past season.
"It comes down to spots," Davis told the Pittsburgh Tribune-Review. "There's only one first baseman on a team. When you have three, there's going to be an odd man out. It was me."