Before joining Fine Gael Hayes had been a member of Democratic Left, a party which he joined because of the hardline anti-Provisional IRA and anti-Irish Republican policies of its leader Proinsias de Rossa. He subsequently joined Fine Gael for similar reasons, this time inspired by the anti-Sinn Féin stance of that party's then leader, John Bruton. In December 1995, he was Nominated by the Taoiseach, John Bruton, to the 20th Seanad, where he was appointed government spokesperson on the Environment. Hayes was first elected to Dáil Éireann at the 1997 general election for the Dublin South-West constituency. He was appointed Fine Gael spokesperson on Housing, House Prices and Urban Renewal.