Born in Dublin on 20th June 1891 to John Costello and Rose Callaghan, Costello was educated in
O'Connell Schools, Richmond Street by the Christian Brothers. At University College Dublin he studied history, languages and literature, obtaining his BA degree in 1911. He obtained his LLB degree in 1914, was called to the inner bar in 1925, and elected a Senior Bencher of the Honourable Society of Kings Inns in 1926. On 31st July 1919 Costello married Ida Mary
O'Malley and they had five children, three sons, Wilfred, Declan and John, and two daughters, Grace and Eavan. In 1922 Costello was appointed as Assistant to the Law Officer of the Provisional Government and between 1922 and 1926 was Assistant to the first Attorney-General of the Free State,
Hugh Kennedy and Kennedy's successor John O'Byrne.
In 1926 Costello was appointed Attorney-General, a position he held until 1932. First elected to
Dáil Éireann in 1933 for the constituency of
County Dublin, he subsequently sat for Dublin Townships and later represented the Dublin South-East constituency. On 27th February 1948 Costello was appointed Taoiseach of an Inter-Party Government, the first of its kind in the Irish State, made up of
Gael, Labour, Clann na Talmhan, Clann
na Poblachta, National Labour and Independents. The coalition remained in power from 1948 to 1951 and is best remembered for the Repeal of the External Relations Act and the formal declaration of the Republic on Easter Monday 1949. Following defeat in the general election of 1951, Costello was asked again, in 1954, to lead the second Inter-Party Government. This second coalition government remained in power until 1957.
In 1959, following
General Richard Mulcahy's resignation as leader of the Fine Gael Party, Costello decided not to offer himself as leader and retired to the backbenches. In addition to serving the needs of his constituents Costello continued to practise at the Bar until a short time before his death on 5th January 1976. He was conferred with honorary degrees from Canadian and American universities, elected a member of the
Royal Irish Academy in 1948 and made a freeman of Dublin City, along with
Valera, in March 1975.
Material relating to his legal career (191468) including the
habeas corpus case, Egan v General McCready (191921); habeas corpus case, General Eoin O'Duffy
(193334); Patrick Kavanagh libel action against The Leader (1954). Correspondence, notes, memoranda, legal opinions, newspaper cuttings relating to the drafting of
amendments to the Constitution and interpretation of the Constitution
(192232). Extensive files concerning Land Purchase Annuities
(192233), Lough Foyle Fishery Rights (192933). Memoranda, notes, correspondence, newspaper cuttings relating to the Imperial Conferences
192632 including material concerning the Privy Council, Inter-Imperial Relations, Colonial Laws Validity Act, Operation of Dominion Legislation. Files, including notes, memoranda, reports, correspondence minutes and various official publications concerning the League Of Nations
Constituency and personal correspondence, departmental and policy files, speeches, addresses, broadcasts, newspaper cuttings, voice recordings relating to the first Inter-Party Government
(19481951). Includes extensive correspondence between Costello and Professor Thomas Bodkin concerning the Lane Pictures controversy
(19481959). Files relating to the Health Bill and 'Mother and Child Scheme'
(195053) and the Baltinglass Sub-Postmastership (195051). Memoranda, correspondence, notes, newspaper cuttings, voice recordings, honorary degrees and memorabilia dating to his official visit to Canada (1948). Also includes film footage of the celebrations in Dublin on 18 April 1949 formally establishing the Republic of Ireland. Copies of minutes, memoranda, correspondence, and audited accounts concerning the Mansion House All-Party Conference on Partition
Constituency and personal correspondence, copies of replies, departmental and policy files, speeches, addresses, broadcasts, newspaper cuttings, voice recordings relating to the second Inter-Party Government
(195457). Material, including memoranda, notes, correspondence, newspaper cuttings, concerning the establishment of an Agricultural Institute
(195056). Includes a lengthy file series entitled 'Taoiseach's Private Papers' containing a diverse range of material covering domestic and foreign issues, policy and current affairs
(195472). Press coverage, copies of speeches, voice recordings, film footage, correspondence, honorary degrees, memorabilia, invitations, photographs dating to his visit to the USA in February 1956.
Policy files, speeches and correspondence dating to both periods in opposition
(195154 and 195759). Includes his letter of resignation as leader of the opposition (1959).
Personal correspondence with Fr Joseph Leonard CM, Wilmarth Sheldon 'Lefty' Lewis and Jacqueline Kennedy (195667). Biographical articles (five part series) by Michael McInerney, Political Correspondent of the
Irish Times marking his retirement from politics. Includes a file of material containing memoranda, notes and correspondence compiled by Costello and including letters and memoranda from former political colleagues offering their recollections of the formation of the first Inter-Party Government (1967-69). Voice recording of the toasts given by Liam Cosgrave, Garret Fitzgerald, Thomas F. O'Higgins, Thomas A. Finlay, Thomas A. Doyle and Alexis Fitzgerald and a reply by Costello at a presentation evening in Jury's Hotel hosted by the Dublin South-East Constituency (1969). Includes other biographical sketches, newspaper cuttings marking his completion of 50 years at the Bar (1964) and his 74th birthday (1965).