Gladstone served on the City Council of Bridgeport, first elected in 1955, serving as minority leader. He was elected to the state senate in 1958 while still serving on the Common Council, as president. In the state senate, he served on the Public Utilities Commission and Cities, Boroughs, Roads and Bridges Committee. During his time in the state senate he also served a term as majority leader. Gladstone also served as Comptroller of Connecticut from 1967 to 1970.