George Henry Robert Charles William Vane-Tempest, 5th Marquess of Londonderry KP (26 April 1821 – 6 November 1884), styled Viscount Seaham between 1823 and 1854 and known as The Earl Vane between 1854 and 1872, was an Anglo-Irish businessman, diplomat and Conservative politician.
Born George Vane, he was the eldest son of Charles Vane, 3rd Marquess of Londonderry, by his second wife Frances Anne, daughter and heiress of Sir Henry Vane-Tempest, 2nd Baronet. He was the nephew of the second Marquess, better known as the statesman Lord Castlereagh, and the half-brother of the fourth Marquess.
He was educated at Eton and Balliol College, Oxford. He became known by the courtesy title Viscount Seaham in 1823 when his father was created Earl Vane and Viscount Seaham, with remainder to the sons by his second wife.
Lord Seaham entered the 1st Life Guards, purchased a lieutenancy on 7 February 1845, and retired on 5 May 1848. He was returned to parliament for Durham North in 1847, a seat he held until 1854, when he succeeded his father as Earl Vane and entered the House of Lords.
In 1867 he was sent on a special mission as Envoy Extraordinary to Russia to Emperor Alexander II, to invest the emperor with the Order of the Garter.
When his half-brother died childless in 1872 he inherited the marquessate and family estates. Two years later he was appointed a Knight of the Order of St Patrick. In 1880 he became Lord-Lieutenant of County Durham, a post he held until his death four years later.
Lord Londonderry managed his father-in-law's estates, which included some of the slate quarries around Corris, and was one of the original promoters of the Corris Railway, created to carry the slate from the quarries to the markets. He sat on the board of the Cambrian Railways, latterly as Chairman.
He married Mary Cornelia Edwards, daughter of Sir John Edwards, 1st Baronet, on 3 August 1846. They set up home at Plas Machynlleth, the Edwards family seat, and had six children.