Sweeney, 28, came up through the Chicago White Sox farm system after being drafted in the second round of the 2003 amateur draft. He was released by the Red Sox on March 30 after posting a .217 average with a .547 OPS in 52 Grapefruit League plate appearances this spring.
After spending two seasons with the White Sox major league club, he then spent four years with Oakland before joining the Red Sox in 2012. A career .280/.338/.378 hitter, Sweeney will give organizational depth in the outfield, joining the likes of Brett Jackson, Brian Bogusevic and Darnell McDonald at Triple-A Iowa to begin the season.
In eight career at-bats at Wrigley Field, Sweeney has just one hit, with a pair of strikeouts.