Frederick Stewart, 4th Marquess of Londonderry

The Most Honourable The Marquess of Londonderry KP PC
Frederick William Robert Stewart, 4th Marquess of Londonderry KP, PC (1805 – 1872), Viscount Castlereagh (1822-1854) (Simon Jacques Rochard, 1833)
Vice-Chamberlain of the Household
In office 29 December 1834 – 8 April 1835
Monarch	William IV
Prime Minister	Sir Robert Peel, Bt
Preceded by	The Earl of Belfast
Succeeded by	Lord Charles FitzRoy
Personal details
Born	7 July 1805 Grosvenor Square, Mayfair, London
Died	25 November 1872 (1872-11-26) (aged 67) White Rock Pavilion, Hastings, Sussex
Nationality	British
Political party	Tory
Spouse(s)	Lady Elizabeth Jocelyn (1813–1884)

Frederick William Robert Stewart, 4th Marquess of Londonderry KP PC (7 July 1805 – 25 November 1872), styled Viscount Castlereagh between 1822 and 1854, was a British nobleman and Tory politician. He was briefly Vice-Chamberlain of the Household under Sir Robert Peel between December 1834 and April 1835.

Stewart was born at Grosvenor Square, Mayfair, London, the eldest son of Charles Stewart, 3rd Marquess of Londonderry, by his first wife Lady Catherine Bligh, daughter of John Bligh, 3rd Earl of Darnley. His mother died when he was seven and while his father was serving in the army overseas, Stewart was looked after by his uncle and aunt, Lord and Lady Castlereagh. He went to Eton in 1814, where he stayed until 1820. After his father succeeded to the marquessate of Londonderry in 1822, Stewart became known by the courtesy title Viscount Castlereagh.

Lord Castlereagh sat as Member of Parliament for County Down from 1826 to 1852. He served under the Duke of Wellington as a Lord of the Admiralty from 1828 to 1830 and under Sir Robert Peel as Vice-Chamberlain of the Household from December 1834 to April 1835. On 23 February 1835 he was sworn of the Privy Council. He was one of the Members of Parliament for County Down from 1826 until 1852. By the latter year, he "had fallen out with his father, the Marquess of Londonderry over their views on the land question [and] was obliged to retire because of these differences". From 1845 until 1864 he was Lord Lieutenant of Down. In 1856 he was made a Knight of the Order of St Patrick.