Fox appeared in 27 games with Baltimore last season, batting .246 with a pair of homers and six runs batted in. He spent most of the campaign at Triple-A Norfolk.
The 29-year-old journeyman began his big league career with the Cubs in 2007 and has also played for Oakland. He belted 11 homers and drove in 44 runs in 82 games for Chicago in 2009, and is a career .237 hitter in 193 major league games.
Pittsburgh also signed outfielder Brandon Boggs and pitcher Shairon Martis to minor league deals with spring training invites. Boggs had two homers in 16 games for Milwaukee last season and has hit .209 in 130 games for the Rangers and Brewers over parts of four seasons. Martis hasn't pitched in the majors since 2009 with Washington and has a record of 6-6 with a 5.33 earned run average in 20 games, including 19 starts over parts of two seasons.
The Pirates also signed infielder Stefan Welch and pitchers Kyle Cofield and Jose Diaz to minor league contracts.