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 seen as less successful than his predecessor Lord Rugby in establishing friendly relations with members of the Irish Cabinet). 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 CIE in the 1935 New Year Honours, CSI in the 1938 New Year Honours and knighted KCIE in 1941. He was further appointed KCMG in the 1948 New Year Honours, GCMG in the 1953 Coronation Honours and 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.
- Maclagan, Michael. "Laithwaite, Sir (John) Gilbert". Oxford Dictionary of National Biography (online ed.). Oxford University Press. doi:10.1093/ref:odnb/39882. (Subscription or UK public library membership required.)
- "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.
- McCullagh, David A Makeshift Majority - the First Inter-Party Government 1948-1951, Institute of Public Administration Dublin 1998 p.113
- "PRO File: PREM 11 1520". Salaam.co.uk. 1956. Retrieved 2 August 2009.
- "No. 34119". The London Gazette (Supplement). 28 December 1934. p. 7.
- "No. 34469". The London Gazette (Supplement). 31 December 1937. p. 5.
- "No. 35029". The London Gazette (Supplement). 31 December 1940. p. 6.
- "No. 38161". The London Gazette (Supplement). 30 December 1947. p. 6.
- "No. 39863". The London Gazette (Supplement). 26 May 1953. p. 2944.
- "No. 40669". The London Gazette (Supplement). 30 December 1955. p. 3.
John Maffey, 1st Baron Rugby
| UK Representative to Ireland
Himself as British Ambassador to Ireland
Himself as British Representative to Ireland
| UK Ambassador to the Republic of Ireland
Sir Laurence Grafftey-Smith
| UK High Commissioner to the Dominion of Pakistan
Sir Alexander Symon