He was elected to parliament (Dáil) in 1977 and was minister of state in the Department of Taoiseach and Defence, 1982, in Charles Haughey's short-lived minority government. When Fianna Fáil returned to power, he was minister for labour 1987-91 and minister for finance 1991-94. Meanwhile Albert Reynolds had taken over the Fianna Fáil leadership and formed successive coalitions with the Progressive Democrats and Labour. In 1994 Reynolds lost Labour support and was forced to resign. He also surrendered the Fianna Fáil leadership and Ahern was elected as his successor. As prime minister, Ahern became a close ally of British prime minister Tony Blair and US president George W Bush. Ireland entered into NATO's Partnership for Peace without a referendum. And the Ahern government faced fierce domestic criticism when it emerged, in 2003, that US air force troop carriers, en route to Iraq, had been allowed to refuel at Shannon airport, despite strong public opposition to the US invasion of Iraq.

Born in Dublin, Ireland, into a working-class republican nationalist family, his father had fought in the 1919-21 war of independence from Britain and subsequent civil war and supported Eamon de Valera and was a member of the IRA. Ahern was educated at the College of Commerce and University College, Dublin, and qualified and practised as an accountant before becoming active in politics. In 1979 he started serving on Dublin City Council, becoming Lord Mayor 1986-97.