1780 in Great Britain
- Monarch – George III
- Prime Minister – Frederick North, Lord North, (Tory)
- Parliament – 14th then 15th
- 16 January – American Revolutionary War: British naval victory at the Battle of Cape St. Vincent over a Spanish squadron.
- 8 March – American Revolutionary War: the League of Armed Neutrality is formed by Russia to try to prevent the Royal Navy from searching neutral vessels for contraband.
- 26 March – the British Gazette and Sunday Monitor, the first Sunday newspaper in Britain, begins publication.
- 4 May – the first Epsom Derby horse race is run on Epsom Downs, Surrey. The victor is Diomed.
- 12 May – American Revolutionary War: Charleston, South Carolina is taken by British forces.
- 2 June – an Anti-Catholic mob led by Lord George Gordon marches on Parliament leading to the outbreak of the Gordon Riots in London.
- 7 June – the Gordon Riots are ended by the intervention of troops. About 285 people are shot dead, with another 200 wounded and around 450 arrested.
- July – Robert Raikes initiates a Sunday school movement, in Gloucester.
- 10 July – American Revolutionary War: 6,000 French troops led by Jean-Baptiste Donatien de Vimeur, comte de Rochambeau land in Newport, Rhode Island but are pinned down by the British.
- September – outbreak of the Second Anglo-Mysore War in India.
- 9 August – American Revolutionary War: Spanish admiral Luis de Córdova y Córdova captures a British convoy totalling 55 vessels amongst Indiamen, frigates and other cargo ships off Cape St. Vincent.
- 16 August – American Revolutionary War: Battle of Camden – the British defeat the Americans near Camden, South Carolina.
- 2 October – American Revolutionary War: British spy John André is hanged by American forces.
- 7 October – American Revolutionary War: Patriot militia defeat the Loyalist militia at the Battle of Kings Mountain.
- 20 November – American Revolutionary War: Britain declares war on the Dutch Republic to stop it from joining the League of Armed Neutrality.
- 20 December – outbreak of the Fourth Anglo-Dutch War.
- The Duke of Richmond calls, in the House of Lords, for manhood suffrage and annual parliaments, which are rejected.
- William Cavendish, 5th Duke of Devonshire, begins development of Buxton Crescent and the Devonshire Royal Hospital to promote Buxton in the Derbyshire Peak District as a spa resort.
- The market town of Middleton, Dorset, is demolished by order of the landowner, Joseph Damer, Lord Milton, and the population moved to a new model village, Milton Abbas.
- The original Craven Cottage is built by William Craven, 6th Baron Craven, in London.
- 25 February – John Sumner, Archbishop of Canterbury (died 1862)
- 21 May – Elizabeth Fry, humanitarian (died 1845)
- 26 December – Mary Fairfax Somerville, mathematician (died 1872)
- 14 February – William Blackstone, jurist (born 1723)
- 12 May – Herod, racehorse (born 1758)
- 18 May – Charles Hardy, governor of Newfoundland (born c. 1714)
- 3 June – Thomas Hutchinson, American-born last governor of Massachusetts Bay Colony (born 1711)
- 4 September – John Fielding, magistrate and social reformer (born 1721)
- 2 October – John André, British Army officer of the American Revolutionary War (executed) (born 1750)
- 17 October – William Cookworthy, chemist (born 1705)
- 26 November – Sir James Denham Steuart, 4th Baronet, economist (born 1712)
- 26 December – John Fothergill, physician (born 1712)
- date unknown – Thomas Dilworth, cleric and writer (year of birth unknown)
- Williams, Hywel (2005). Cassell's Chronology of World History. London: Weidenfeld & Nicolson. p. 333. ISBN 0-304-35730-8.
- Penguin Pocket On This Day. Penguin Reference Library. 2006. ISBN 0-14-102715-0.
- Berry, George (1970). Discovering Schools. Tring: Shire Publications. ISBN 0-85263-091-3.
- Hattendorf, John (2000). Naval Policy and Strategy in the Mediterranean: past, present, and future. Taylor & Francis. p. 37. ISBN 0-7146-8054-0.
- Harbron, John (1988). Trafalgar and the Spanish Navy. Conway Maritime Press. p. 84. ISBN 0-85177-477-6.
- Edler, Friedrich (2001) . The Dutch Republic and The American Revolution. Honolulu: University Press of the Pacific. pp. 163–166. ISBN 0-89875-269-8.
- "Inside Buxton's dome". BBC Derbyshire. June 2003. Retrieved 2012-07-05.