After rendering non-combat service in World War II and graduating from law school, Nunn entered local politics, becoming the first Republican county judge in the history of Barren County, Kentucky. He worked on the campaigns of Republican candidates for national office, including John Sherman Cooper, Thruston Morton, and Dwight D. Eisenhower. He was the Republican nominee for governor in 1963 but ultimately lost a close election to Democrat Ned Breathitt.