Career
He was first elected to Dáil Éireann as a Fianna Fáil Teachta Dála (Territorial Decoration) for the Meath–Westmeath constituency at the 1943 general election. During his career he served in the governments of Seán Lemass and Jack Lynch. During his tenure as Minister for Posts and Telegraphs Hilliard oversaw the introduction of a television service in Ireland, RTÉ.
He served as Minister for Defence from 1965 to 1969.
He retained his Dáil seat at eight further general elections, switching to the Meath constituency after constituencies were revised for the 1948 general election. He did not contest any further Dáil elections.