William Conyngham Greene was born in Ireland, son of Richard Greene, barrister and writer, and the Hon. Louisa Plunket; his grandfathers were the eminent judge Richard Wilson Greene and John Plunket, 3rd Baron Plunket. He was named after his uncle William Greene, Dean of Christ Church Cathedral, Dublin, but did not use the name William as an adult. He was educated at Harrow School and Pembroke College, Oxford.
Greene entered the Foreign Office in 1877, was posted as Acting Third Secretary to Athens in 1880, and acted as Chargé d'Affaires at Stuttgart and Darmstadt 1883–87. He transferred formally to the Diplomatic Service (then separate from the Foreign Service) in 1877 and was posted as 2nd Secretary at The Hague 1889–91 and at Brussels 1891–93. He was then promoted to be Secretary of Legation at Tehran in 1893 and promoted again to be "HM Agent at Pretoria with rank of Chargé d'Affaires" in 1896.
Pretoria was then the capital of the Transvaal Republic, and on 9 October 1899 the Transvaal government handed to Conyngham Greene an ultimatum stating that if in 48 hours British troops did not retire from the border, a state of war would exist. The British government replied that the conditions imposed by the Transvaal were such that the British government could no longer discuss the subject, and the Second Boer War began on 11 October. On that day Conyngham Greene left Pretoria, and on his arrival at Cape Town a few days later he "was accorded a magnificent reception. A crowd of 3,000 persons who had gathered sang 'Rule, Britannia' and 'God Save the Queen'."
In 1901 Greene was appointed Minister to the Swiss Confederation. While stationed in Berne he was treasurer of an Appeal Fund set up in 1904 for building a new church, which became the Anglican church of Saint Ursula in Berne. He remained at Berne until December 1905 and was appointed Minister to Romania in January 1906. In January 1911 he was transferred to Copenhagen as Minister to Denmark where he stayed only two years. In December 1912 he was made a Privy Counsellor and posted as Ambassador to Japan. He was the King's representative at the enthronement of the Taishō Emperor in 1915. His obituary in the Times of London wrote that "He remained in Tokyo until the end of the First World War and proved himself a great Ambassador. His open and genial manner won the confidence of the Japanese, and retained it throughout all the vicissitudes of the War and in spite of certain difficulties with the Ministry for Foreign Affairs in Tokyo. His departure in April 1919 was universally regretted." Sir Conyngham (as he had become) and Lady Lily Greene were among the passengers who landed from the Aquitania at Plymouth on 10 May 1919.
Conyngham Greene was appointed CB in the 1897 New Year Honours. On his return from South Africa he was knighted KCB in the 1900 Queen's Birthday Honours – the list mentioned that he was "late British Agent at Pretoria". While serving in Japan he was appointed KCMG. In 1917 he was made an honorary fellow of his old college, Pembroke College, Oxford.
In 1884, while at the Legation at Stuttgart, Conyngham Greene married Lady Lily Frances Stopford, daughter of the 5th Earl of Courtown. She died in 1950.
Some of Greene's writings were posthumously published.
- Foreign Office files for Japan and the Far East (1991)
- "No. 24518". The London Gazette. 2 November 1877. p. 5997.
- "No. 24818". The London Gazette. 27 February 1880. p. 1720.
- "No. 26461". The London Gazette. 24 November 1893. p. 6757.
- "No. 26774". The London Gazette. 4 September 1896. p. 4987.
- The Times, London, 27 August 1896, p.3
- Boer War – Path to War, globalsecurity.org
- John P. Wisser, The second Boer War, 1899–1900, Hudson-Kimberley, Kansas City, Mo., 1901, p.16
- Conyngham Greene at Cape Town, New York Times, 16 October 1899
- "No. 27314". The London Gazette. 17 May 1901. p. 3379.
- St Ursula's Church, Berne – History
- "No. 27874". The London Gazette. 12 January 1906. p. 285.
- "No. 12325". The Edinburgh Gazette. 31 January 1911. p. 103.
- "No. 28672". The London Gazette. 17 December 1912. p. 9561.
- Embassy & Consular Archives – Japan (1905–1940)
- The Times, London, 11 November 1915, p.7
- Obituary, The Times, London, 3 July 1934, p.9
- The Times, London, 12 May 1919, p.18
- "No. 26810". The London Gazette. 1 January 1897. p. 65.
- "No. 27200". The London Gazette. 8 June 1900. p. 3630.
- "No. 28842". The London Gazette (Supplement). 22 June 1914. p. 4878.
- WorldCat Identities Archived 30 December 2010 at the Wayback Machine.: Greene, William Conyngham Sir 1854–1934
- GREENE, Rt Hon. Sir Conyngham, Who Was Who, A & C Black, 1920–2008; online edn, Oxford University Press, Dec 2007, accessed 17 April 2012
- Rt. Hon. Sir William Conyngham Greene – thepeerage.com
- Ian Nish (2004) British Envoys in Japan 1859–1972 Folkestone, Kent: Global Oriental. ISBN 9781901903515; OCLC 249167170
Frederick Robert St John
|Envoy Extraordinary and Minister Plenipotentiary to the Swiss Confederation
Sir George Bonham, 2nd Baronet
|Envoy Extraordinary and Minister Plenipotentiary at the Court of His Majesty the King of Roumania
Hon. Sir Alan Johnstone
|Envoy Extraordinary and Minister Plenipotentiary to His Majesty the King of Denmark
Sir Henry Lowther
Sir Claude MacDonald
|Ambassador Extraordinary and Plenipotentiary to His Majesty the Emperor of Japan
Sir Charles Eliot