In a corresponding move, the A's designated right fielder Andrew Brown for assignment. The two teams are also exchanging international slot money.
Davis, 27, was designated for assignment on Thursday in a move that cleared the way for Pedro Alvarez to play first base full time next season. The Pirates acquired Davis in April via a trade with the New York Mets. Platooning with Gaby Sanchez at first base the rest of the season, Davis hit .235 with 10 home runs and 46 RBI in 131 games.
In five seasons, Davis has hit .240 with with 78 homers and and 270 RBI. He finished seventh in the 2010 Rookie of the Year voting with the Mets, and also hit 32 home runs with 90 RBI in 2012.
Oakland also signed free-agent first baseman Billy Butler last week. According to Susan Slusser of the San Francisco Chronicle, signing Davis is largely a depth move that also provides some roster flexibility for the A's.
Oakland finished 88-74 in 2014, second in the AL West, before losing 9-8 to the Kansas City Royals in the AL Wild Card game on Sept. 30.
Pittsburgh also finished 88-74, second in the NL Central, before losing 8-0 to the eventual World Series champion San Francisco Giants in the NL Wild Card game on Oct. 1.
- Mike Fiammetta