Republican politician Thomas Evert Petri was born in Marinette, Wisconsin, on May 28, 1940. His father, Thomas Evert, was killed during World War II and after his mother remarried he was legally adopted by his stepfather Robert Petri.
Petri graduated from Fond du Lac public schools and attended Harvard University, earning a BA in 1962 and a JD in 1965. While still a student, Petri helped to found the Ripon Society, a centrist Republican organization. After his graduation he returned to Wisconsin to clerk for Judge James Doyle for a year. He then satisfied a long-standing desire to volunteer for the Peace Corps. When Petri returned to the United States from Somalia he served as executive director of the Ripon Society and conducted seminars on elections at the Kennedy Institute. From 1969 to 1970 he was in Washington, D.C. as director of the crime and drug studies section of the President's National Advisory Council on Executive Organization.
After establishing a law practice in Fond du Lac, Petri was elected to the Wisconsin State Senate in 1972 and re-elected in 1976. During this period his chief committee assignments included vice-chairmanships of Industry, Labor, Taxation, and Banking (1973) and the Legislative Council's Special Committee on Solid Waste Management (1977). He also served on the Joint Committee on Audit, the Council on Drug Abuse, and other committees noted in biennial editions of the Blue Book. In 1975 while continuing to serve in the Senate, Petri was a fellow at the Woodrow Wilson Center for International Studies.
Generally regarded as a moderate Republican, Petri earned his reputation in Wisconsin not for specific legislative initiatives, but by his willingness to run for elective office. In 1974 he undertook an apparently hopeless contest with Senator Gaylord Nelson. In 1978 he expressed interest in both the governor's race and the lieutenant governorship but failed to win party support for either. In 1979 Petri was elected to the United States Congress in a special election to fill the unexpired seat of the late William Steiger, with whom he had been closely aligned philosophically.
