Irish politician, prime minister from February 1973 to July 1977.

His father, W.T. Cosgrave, was president of the Executive Council and head of the government of the Irish Free State during the first 10 years of its existence (1922–32). Liam, the elder son, was educated at Castlenock College, Dublin, and King's Inns, studied law, and was called to the Irish bar in 1943. In that same year he entered the Dáil (Irish parliament), and he retained his seat until his retirement from politics in 1981. In 1948, when the first interparty government replaced Eamon De Valera's Fianna Fáil regime, which had been in power for the previous 16 years, Cosgrave became parliamentary secretary to the taoiseach (prime minister) and to the minister for industry and commerce. It was a short-lived administration, going out of power after three years, in 1951. But it was back again in 1954 for another three years, at which time Cosgrave became minister for external affairs and led the first Irish delegation to the United Nations General Assembly in 1956.

Cosgrave succeeded James Dillon as leader of the Fine Gael party in 1965 and eight years later, in coalition with the Labour Party, secured the prime ministry. His National Coalition was defeated in the general elections of June 1977, largely on the economic issues of inflation and unemployment.