Sir William Conyngham Greene, GCMG, KCB, PC (29 October 1854 – 30 June 1934) was a British diplomat who served as minister to Switzerland, Romania and Denmark, and as ambassador to Japan.

[15] According to Greene's obituary in the Times of London, "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.

[18] 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".

In 1884, while at the Legation at Stuttgart, Conyngham Greene married Lady Lily Frances Stopford, daughter of the 5th Earl of Courtown.

They had four children, Barrington, Geoffrey, Kathleen, who was a well-known author of children's books, and Norah, who married Sir Hubert Brand, younger son of Henry Robert Brand, 2nd Viscount Hampden and died in 1924, leaving issue.