In 1954 Sheehy Skeffington moved into formal parliamentarian politics when was elected as a member of the 8th Seanad Éireann by the Dublin University constituency, thus beginning a long career as one of the leading lights of the Irish Senate. He was re-elected in 1957, but lost his seat in 1961. He was returned to the 11th Seanad in 1965 and was re-elected for a final time in 1969. In the Seanad he was known as a champion of civil liberties and an opponent of authoritarianism.