- 1 January
- Legislative union of Great Britain and Ireland completed under the Act of Union 1800, bringing about the United Kingdom of Great Britain and Ireland and abolition of the Parliament of Ireland. A revised flag of the United Kingdom is adopted from this date.
- First one-inch-to-the-mile (1:63,360 scale) map based on the work of the Ordnance Survey is published, covering the county of Kent.
- 14 January – Britain places embargoes on vessels of the Second League of Armed Neutrality of the North.
- 2 February – Parliament of the United Kingdom meets for the first time.
- 5 February – William Pitt the Younger tenders his resignation as Prime Minister of the United Kingdom.
- 1 March – London Stock Exchange founded as a regulated institution; its new building is completed on 30 December.
- 8 March – second Battle of Abukir: a British Army under Ralph Abercromby defeats the French troops.
- 10 March – the first British census is carried out. The count is conducted by clergy, overseers of the poor and schoolmasters. The population of England and Wales is determined to be 8.9 million, with London revealed to have 860,035 residents.
- 14 March – William Pitt the Younger resigns over Catholic Emancipation, having first tendered his resignation on 5 February.
- 16 March – Edinburgh music teacher Anne Gunn is granted the first British patent for a board game, designed as a music teaching aid.
- 17 March – Henry Addington, 1st Viscount Sidmouth becomes Prime Minister.
- 21 March – Battle of Alexandria: Abercromby's forces defeat those of the French in the Egyptian city of Alexandria.
- 2 April – Battle of Copenhagen in the War of the Second Coalition: The Royal Navy under Admiral Sir Hyde Parker forces the Royal Dano-Norwegian Navy to accept an armistice. Vice-Admiral Horatio Nelson leads the main attack, deliberately disregarding his commander's signal to withdraw.
- 19 May – Nelson is created Viscount Nelson of the Nile, and of Burnham Thorpe in the County of Norfolk, for his part in the strategic victory at Copenhagen.
- 18 June – Cairo falls to British troops.
- 6 July – Battle of Algeciras: The French fleet achieves victory over the British.
- 12 July – Second Battle of Algeciras: The British fleet defeats the French and Spanish.
- 18 July – Matthew Flinders sets out on a voyage to produce a detailed survey of the coastline of Australia, the southern coast of which is still unknown.
- 30 September – the Treaty of London is signed for peace between the First French Republic and the United Kingdom as a preliminary to the Treaty of Amiens.
- 24 November – title Duke of Sussex first conferred, on Prince Augustus Frederick.
- 26 November – Charles Hatchett announces his discovery of the chemical element niobium to the Royal Society.
- 24 December – Richard Trevithick demonstrates the first steam-powered vehicle to carry passengers at Camborne.
- Dalton's law: John Dalton observes that the total pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of each individual component in a gas mixture.
- Thomas Young discovers the interference of light.
- Maria Edgeworth's novel Belinda is published.
- Henry James Pye's epic poem Alfred is published.
- 219 people are hanged this year in England and Wales, a record for any year after 1785.
- 4 January – James Giles, painter (died 1870)
- 14 January – Jane Welsh Carlyle, letter–writer (died 1866)
- 2 February
- 7 February – John Rylands, weaver, entrepreneur and philanthropist (died 1888)
- 13 February – Henry Bulwer, 1st Baron Dalling and Bulwer, politician, diplomat and writer (died 1872)
- 21 February – John Henry Newman, Roman Catholic Cardinal, canonised (died 1890)
- 24 April – Robert Grosvenor, 1st Baron Ebury, politician (died 1893)
- 28 April – Anthony Ashley-Cooper, 7th Earl of Shaftesbury, politician and philanthropist (died 1885)
- 9 May – Samuel Cousins, engraver (died 1887)
- 4 June – James Pennethorne, architect (died 1871)
- 10 June – Joseph Rowntree, educationist (died 1859)
- 24 June – Caroline Clive, author (died 1873)
- 15 August – Charles Elliot, naval officer, diplomat and colonial administrator (died 1875)
- 27 December – Charles Clay, surgeon (died 1893)
- date unknown – Charles George James Arbuthnot, general, born at sea (died 1870)
- 28 March – Ralph Abercromby, general (born 1734)
- 2 April – Thomas Dadford, Jr., engineer (year of birth unknown)
- 3 May (bur.) – Mary Lacy, shipwright and naval pensioner (born c.1740)
- 17 May – William Heberden, physician (born 1710)
- 14 June – Benedict Arnold, spy and Army officer (born 1741 in Connecticut Colony)
- 7 July – William Legge, 2nd Earl of Dartmouth, statesman (born 1731)
- 9 September – Gilbert Wakefield, scholar (born 1756)
- Autumn – David Levi, scholar (born 1742)
- Everett, Jason M., ed. (2006). "1801". The People's Chronology. Thomson Gale.
- Groom, Nick (2007) . The Union Jack: the Story of the British Flag. London: Atlantic Books. p. 203. ISBN 978-1-84354-337-4.
- Penguin Pocket On This Day. Penguin Reference Library. 2006. ISBN 0-14-102715-0.
- "Chronology of State Medicine". Archived from the original on 9 August 2007. Retrieved 10 August 2007.
- Raz, Carmel (2018). "Anne Young's Musical Games (1801): Music Theory, Gender, and Game Design". SMT-V. Society for Music Theory. 4 (2).
- "No. 15366". The London Gazette. 19 May 1801. p. 549.
- "British History Timeline, BBC History". Archived from the original on 22 September 2007. Retrieved 10 August 2007.
- The Hutchinson Factfinder. Helicon. 1999. ISBN 1-85986-000-1.
- Leavis, Q. D. (1965). Fiction and the Reading Public (rev. ed.). London: Chatto & Windus.
- Cox, Michael, ed. (2004). The Concise Oxford Chronology of English Literature. Oxford University Press. ISBN 0-19-860634-6.
- "1800-1827 Public executions". capitalpunishmentuk. Retrieved 13 October 2019.