In 1972, Vainisi began his career with the Bears as the club's controller. His later titles included treasurer and in-house counsel prior to serving as the general manager from 1983-1987.
The Chicago Bears had a record of 47-17 during Vainisi's tenure and fielded arguably one of the greatest teams the league has seen in 1985.
After his time in Chicago, Vainisi worked for the Lions and then helped create and head the football operations for the World League of American Football. Vainisi's career continued after football when he took over Hinshaw & Culbertson's sports and entertainment law division in Chicago. He then bought Forest Park Bank before becoming its chairman and CEO.