On August 24, 1983, Vainisi replaced Jim Finks as the general manager of the Bears,[7] and was general manager for the Bears for their only Super Bowl win in 1985 when the Bears defeated the New England Patriots in Super Bowl XX.[8] He was one of the people responsible for the removal of the Bears cheerleading squadChicago Honey Bears in 1985, saying that the squad might be replaced by a high school band, despite not having done so.[9] His close relationship with then-head coach Mike Ditka factored in his firing by Bears president Michael McCaskey on January 15, 1987. The rift stemmed from Vainisi and Ditka persuading McCaskey to acquire Doug Flutie, who was the starting quarterback in the Bears' 27–13 divisional playoff loss to the Washington Redskins at Soldier Field on January 3. The Bears dismissed Vainisi twelve days after the loss.[10] He was the last Bears general manager until Jerry Angelo took over in 2001.[11]
In 1987, Vainisi became the vice president of player personnel for the Detroit Lions.[12] He drafted Hall of Fame running back Barry Sanders in the 1989 NFL draft. Vainisi left the Lions in 1990 to create and head the football operations of the World League of American Football (later named NFL Europe).[13] In 1995, Vainisi retired from professional football and joined the Chicago law firm Hinshaw & Culbertson, heading the sports and entertainment division. He worked as a sports agent through Hinshaw & Culbertson and bought Forest Park National Bank.[14]