| Rank: | 2nd | |
| First Term: | February 18 1948 - June 13 1951 | |
| Second Term: | June 2 1954 - March 20 1957 | |
| Predecessor: | Eamon de Valera | |
| Successor: | Eamon de Valera | |
| Date of Birth: | 20 June 1891 | |
| Date of Death: | 5 January 1976 | |
| Place of Birth: | Dublin, Ireland | |
| Profession: | Lawyer | |
| Political Party: | Fine Gael | |
John Aloysius Costello was born on 20 June 1891 in Dublin. He graduated from University College Dublin with a degree in modern languages and law. In 1914 he was called to the bar and became a barrister. In 1922 he joined the staff of the Attorney-General and in 1926 he was appointed the Attorney-General by the Cumann na nGaedhael government. He also represented the Irish Free State at Imperial Conferences and League of Nations meetings.
In 1933 Costello was elected to Dáil Éireann for the very first time. In 1948 he was asked to become Taoiseach in the first Inter-Party government. Richard Mulcahy, the leader of Fine Gael, was seen as an unacceptable choice for Taoiseach. Costello was seen as the one person who could unite the different elements that were to make up the new government. This government oversaw two significant events: the decalaration of the Republic and the Mother and Child Scheme. At a press conference in Canada on 7 September 1948 Costello announced that the Irish Free State was about to leave the Commonwealth. On 18 April 1949 (Easter Monday) the Republic of Ireland came into existence. In 1950 the Minister for Health, Noel Browne, tried to introduce a scheme which would provide free health care for children up to the age of sixteen. The Mother and Child Scheme was opposed by the Catholic Bishops and the Irish dictors and Browne resigned as minister. The episode damaged the government and in May 1951 Costello requested that the Dáil be dissolved and an election was called.
In May 1954 Fianna Fáil lost power and Costello returned as Taoiseach and head of another Inter-Party government. The government had a comfortable majority in the Dáil, but an outbreak of militant activity by the IRA de-stabilised the government. Clann na Poblachta and Fianna Fáil tablied motions of no confidence in Costello's leadership. Rather than face defeat he asked the President to dissolve the Dáil again. In 1957 Fianna Fáil returned to power and Costello returned to the bar and retired to the backbenches of Dáil Éireann. Costello received many honorary degrees from universities in the United States and eleswhere. In March 1975 Costello was made a freeman of the city of Dublin.
John A. Costello died on 5 January 1976.
| Preceded by: Eamon de Valera Taoiseach (1932-1948) |
Prime Ministers of Ireland Taoisigh na hÉireann |
Succeeded by: Eamon de Valera Taoiseach (1951-1954) |