After completing undergraduate studies, Simonson worked for several years on Wall Street before returning to Wisconsin to pursue a law degree. Simonson worked his way through law school at the Wisconsin Department of Corrections. Upon graduation he was hired as Deputy Counsel to the Governor, and was soon promoted to Legal Counsel to Wisconsin Governor Tommy Thompson, a post he held from 1995 to 1999. Under Thompson, Simonson served as Chair of the state Pardon Advisory Board, directed the Governor's emergency management efforts, directed the policy development for crime and corrections, and coordinated the state's public safety agencies.