Madigan was founder and continues as senior partner of the law firm Madigan and Getzendanner, specializing in corporate real estate property tax appeals, which has been accused of profiting from Madigan's position and power. Getzendanner and four other staff attorneys handle the tax appeals, while Madigan brings in clients. In 2008 Madigan and Getzendanner represented 45 of the 150 most valuable buildings in downtown Chicago, more than any other property tax appeal firm, and more than twice as many as the second-highest. Clients include the John Hancock Center and the Prudential Plaza. From 2006 to 2008 in Cook County, Illinois, Madigan and Getzendanner received the largest reductions for their clients of any tax appeal law firm. Venues for property tax appeals law firms in Cook County include hearings before the County Assessor, the County Board of Review, and the County courts. Judges in Illinois are elected in partisan elections, and Madigan, by his Democratic Party leadership roles as committeeman and state chairman, is one of the main persons involved in slating judicial candidates.
