An intimidating defender, the Afro-coiffed 6-foot-9 center averaged 7.3 points, 11.3 rebounds, 2.2 blocked shots and 1.8 steals for the Detroit Pistons last season. Wallace, 31, has averaged 6.6 points, 10.7 rebounds and 2.2 blocked shots during his 10-year career, helping Detroit to the 2004-05 NBA championship.
"We are thrilled that Ben is now officially a Bull," said Bulls General Manager John Paxson, as he introduced Wallace to the media at the United Center.
Wallace, a four-time winner of the Defensive Player of the Year Award, is expected to dominate the interior for the Bulls, who have been eliminated early in playoffs the last two seasons.
The Chicago Sun-Times said Wallace's four-year deal is worth nearly $60 million.