The title of Marquess of Londonderry (pronounced "Lundundry") is a title in the Peerage of Ireland created in 1816 for Robert Stewart, 1st Earl of Londonderry, father of Lord Castlereagh, the Foreign Secretary at the time.
The Marquess holds the subsidiary titles of Earl of Londonderry (Irish, 1796), Earl Vane (Peerage of the United Kingdom, 1823), Viscount Castlereagh (Irish, 1795), Viscount Seaham, of Seaham in the County of Durham (UK, 1823), Baron Londonderry (Irish, 1789), and Baron Stewart, of Stewart's Court and Ballylawn in the County of Donegal (U.K. 1814). The two United Kingdom titles were created separately for Charles William Vane, who would later become the third Marquess. The remaining titles were all created for Robert Stewart, the 1st Marquess. Stewart was one of the few people to become a Marquess without inheriting any titles prior to the creation.
The title Earl Vane were created for the third Marquess with special remainder to pass to his sons by his second wife, whilst the Marquessate and Baron Stewart passed to his son by his first wife. In 1872 the titles were reunified.
Between 1823 and 1854 and between 1872 and 1999, the Marquesses of Londondery sat in the House of Lords as The Earl Vane. Between 1822 and 1823 and between 1854 and 1872, they sat as The Lord Stewart.
Marquesses of Londonderry (1816)
- Robert Stewart, 1st Marquess of Londonderry (1739-1821), elected a Representative Peer in 1800
- Robert Stewart, 2nd Marquess of Londonderry (1769-1822), the statesman known to historians as Lord Castlereagh
- Charles William Vane, 3rd Marquess of Londonderry (1778-1854)
- Frederick William Robert Stewart, 4th Marquess of Londonderry (1805-1872)
- George Henry Robert Charles William Vane-Tempest, 5th Marquess of Londonderry (1821-1884)
- Charles Stewart Vane-Tempest-Stewart, 6th Marquess of Londonderry (1852-1915)
- Charles Stewart Henry Vane-Tempest-Stewart, 7th Marquess of Londonderry (1878-1949)
- Edward Charles Stewart Vane-Tempest-Stewart, 8th Marquess of Londonderry (1902-1955)
- Alexander Charles Robert Vane-Tempest-Stewart, 9th Marquess of Londonderry (b. 1937)
