Humphrey Trevelyan, Baron Trevelyan, KG, GCMG, CIE, OBE (27 November 1905 – 9 February 1985) was a British diplomat and author.

Trevelyan was a son of Reverend George Trevelyan, grandson of the Venerable George Trevelyan, Archdeacon of Taunton, third son of Sir John Trevelyan, 4th Baronet. He was educated at Lancing College and Jesus College, Cambridge. After Cambridge Trevelyan joined the Indian Civil Service. He served in India until independence in 1947, then transferred to HM Diplomatic Service. He held many key diplomatic posts, including charge in Beijing after the Revolution, ambassador to Egypt at the time of Suez, ambassador to Iraq at the time of the 1961 Kuwait crisis, Iraq's first attempt to annex Kuwait, and ambassador to the Soviet Union. He completed forty years of public service as the last high commissioner of Aden, where he wound up British rule and oversaw the British withdrawal from what had been the Aden Protectorate and became South Yemen.

Trevelyan wrote a number of books about his career, including The India We Left.

In 1968, he was elevated to the House of Lords as a life peer with the title Baron Trevelyan, of Saint Veep in the County of Cornwall.