The Braves, who hold a healthy lead in the wild card standings, also obtained outfielder Matt Diaz earlier in the day from Pittsburgh. Atlanta is 7 1/2 games behind Philadelphia for first place in the NL East.
Wilson, who is currently on the 15-day disabled list with a bruised left heel, hit .249 with 11 RBI in 62 games for Seattle this season.
It will mark a return to the National League for the 33-year-old Wilson, who played for Pittsburgh from 2001-09. He's a career .266 hitter with 61 homers and 422 RBI.