The announcement was made by Executive Vice President/General Manager Ben Cherington.
Sweeney, 26, hit .265 (70-for-264) with 11 doubles, three triples, one home run, 25 RBI, 34 runs scored and 33 walks in 108 games with the Athletics in 2011, appearing at all three outfield positions and designated hitter. The left-handed hitter batted at a .286 clip (63-for-220) off right-handers last season. He did not commit an error in 153 total chances in the outfield, his second straight errorless campaign (also 153 chances in 2010).
The Red Sox acquired Sweeney from the Oakland Athletics with right-handed pitcher Andrew Bailey on December 28 in exchange for outfielder Josh Reddick and minor leaguers right-handed pitcher Raul Alcantara and first baseman Miles Head. A second-round selection of the Chicago White Sox in the 2003 First-Year Player Draft, Sweeney has a career .283 average (428-for-1515) with 83 doubles, 10 triples, 14 home runs, 169 RBI, 202 runs and 139 walks in 472 career Major League games over parts of six seasons with the White Sox (2006-07) and Athletics (2008-11).