In 1954, at the age of 26, Rock was elected to the Indiana House of Representatives as a Democrat serving in the 1955, 1959, 1961, and 1963 sessions. Then he served as Lieutenant Governor of Indiana from 1965 to 1969. In 1968, Rock won the Democratic nomination for Governor of Indiana, but lost the general election to Republican Secretary of State Edgar Whitcomb. He later served as Mayor of Anderson, Indiana from 1972 to 1980, where he established the Anderson Housing Authority Commission and the City of Anderson Transportation System (CATS).
