Delahey originally contained several farming properties. The Government acquired the land in the mid-to-late 1980s for re-subdivision as mostly residential properties. The suburb is named after William Delahey, who whilst still a baby had arrived from Ireland with siblings and parents Henry Delahey and Mary (née Dodd) in June 1840. Mr. William Delahey had been connected with the Keilor Shire Council for eighteen years and was elected as president during the year 1882–83. The suburb's name was formally adopted in 1994.