1815 in the United Kingdom

January to June

• 2 January
  • Lord Byron marries Anna Isabella Milbanke at Seaham, County Durham.
  • The Prince Regent divides the Order of the Bath into three classes: the Knights Grand Cross, Knights Commander and Companions.^[1]
• 3 January – Austria, Britain and Bourbon-restored France form a secret defensive alliance treaty against Prussia and Russia.
• 8 January – War of 1812: Battle of New Orleans – American forces under General Andrew Jackson defeat the British in the last major battle of the war.^[1]
• 16 January–15 February – Lieutenant-General Sir John Murray, 8th Baronet, MP, is court-martialed and admonished for his conduct before Tarragona in the Peninsular War;^[2] he will be the most senior officer so to appear until 2021.
• 13 February – The Cambridge Union Society, one of the oldest debating societies in the world, founded at the University of Cambridge.
• 15 March – Importation Act, first of the Corn Laws, passed by Parliament, preventing the import of cheap foreign grain.^[3]
• 29 March – The Duke of Wellington leaves Vienna, where he has been leading Britain's delegation at the Congress of Vienna, to take command of British and allied army gathering near Brussels
• 30 May – The East Indiaman Arniston, repatriating wounded troops to Britain from Ceylon, is wrecked near Waenhuiskrans, South Africa with the loss of 372 of the 378 on board.
• 16 June – Napoleonic Wars: Battle of Quatre Bras – Marshal Ney wins a strategic victory over an Anglo-Dutch force.
• 18 June – Napoleonic Wars: the Duke of Wellington wins a decisive victory over Napoleon at the Battle of Waterloo.^[4]

• 21 June – News of the victory at Waterloo reaches London from Broadstairs late that evening.^[5]

July to December

• 10 July – Apothecaries Act prohibits unlicensed medical practitioners.^[6]
• 15 July – Napoleon boards HMS Bellerophon off Rochefort and surrenders to Captain Frederick Lewis Maitland of the Royal Navy.
• 24 July–4 August – HMS Bellerophon anchors off the south Devon coast with Napoleon on board prior to his being taken into exile.^[7]
• 31 July – The 1815 Philadelphia train accident, a boiler explosion, kills at least 13 people in County Durham.
• 1 August – William Smith publishes the first national geological map of the UK, A Delineation of the Strata of England and Wales, with part of Scotland.^[8]
• 18 October – The Bible Christian Church, a Wesleyan Methodist denomination, is founded by William O'Bryan in north Devon and Cornwall.
• 3 November – Sir Humphry Davy announces his invention of the Davy lamp as a coal mining safety lamp.^[4][9]
• 5 November – Ionian Islands become a British protectorate.^[6]

Undated

• Jones, Watts and Doulton begin life as a stoneware pottery in South London.
• Wisden Cricketers' Almanack retrospectively recognises statistics for first-class cricket in England from this year.