Helen Thomson was elected in 1974 to the Davis Joint Unified School District Board of Education. She was elected to the Yolo County Board of Supervisors in 1986 and re-elected in 1990 and 1994. She won the seat in the California State Assembly in 1996, and served three terms. In 2002, when her assembly term ended, Thomson again won a seat on the Yolo County Board of Supervisors, and was re-elected without opposition in June 2006.