Gilbert Laithwaite was the eldest of two sons and two daughters, born in Dublin. His father was John Laithwaite of the Post Office survey. His mother was Mary Kearney whose family hailed from Castlerea, Co. Roscommon. Laithwaite was a first cousin of the Irish Republican leader Ernie O'Malley.
Laithwaite went to Clongowes Wood College, where he won a scholarship to Trinity College, Oxford, going on to achieve a second class degree. He received an honorary fellowship from that college in 1955.
In the First world war, Laithwaite served in the British army in France as a second lieutenant with the 10th Lancashire Fusiliers. He was wounded in 1918. In 1971 he published an account of part of his war experience entitled 21 March 1918: Memories of an Infantry Officer.
Work in India followed, on Lord Lothian's Franchise committee, which extended the Indian franchise to 35 million voters. From 1936 to 1943 he was principal private secretary to the Viceroy of India, the second marquess of Linlithgow.
In 1943 he returned to Britain as assistant under-secretary of state for India. In 1947 he took part in London talks on Burmese independence, also attended by Stafford Cripps and Aung San. In 1949 he became United Kingdom representative, and from 1 July 1950 Ambassador, to the Republic of Ireland (where he was generally regarded as less adept than his predecessor Lord Rugby). In 1951 he became high commissioner to Pakistan. In this position he became concerned with the implications of US military aid to Pakistan under Iskander Mirza. He became permanent under-secretary of state for Commonwealth relations from 1955 to 1959, visiting Australia and New Zealand. From 1963 to 1966 he was vice-chairman of the Commonwealth Institute.
Laithwaite was appointed a CIE in the 1935 New Year Honours appointed a CSI in the 1938 New Year Honours and knighted with the KCIE in 1941. He was further appointed a KCMG in the 1948 New Year Honours, a GCMG in the 1953 Coronation Honours and a KCB in the 1956 New Year Honours. In 1960 he was appointed a Knight of Malta. He was president of the Hakluyt Society (1964–69), vice-president of the Royal Central Asian Society (1967) and president of the Royal Geographical Society (1966–69).
- Lysaght, Charles (16 July 2006). "The excellent honour of ambassador suits you, sir". Irish Independent.
- "Michael Maclagan, Laithwaite, Sir (John) Gilbert (1894–1986)". Oxford Dictionary of National Biography. Oxford University Press. 2004. Retrieved 2 August 2009.
- "News of the Day". The Age. 10 September 1954. Retrieved 2 August 2009.
- "London Talks For Independence Begins". Back to the Past-Today – London Tal. 13 January 1947. Retrieved 2 August 2009.
- "PRO File: PREM 11 1520". Salaam.co.uk. 1956. Retrieved 2 August 2009.
John Maffey, 1st Baron Rugby
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Himself as UK Representative to Ireland
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