1778 in Great Britain

• Monarch – George III
• Prime Minister – Frederick North, Lord North (Tory){{cite web |title=History of Lord Frederick North - GOV.UK |url=https://www.gov.uk/government/history/past-prime-ministers/frederick-north |website=www.gov.uk |access-date=1 July 2023 |language=en}}

• 18 January – the third Pacific expedition of James Cook, with ships {{HMS|Resolution|1771}} and {{HMS|Discovery|1774}}, first views Oahu then Kauai in the Hawaiian Islands, which he names the "Sandwich Islands".{{cite book|title=Penguin Pocket On This Day|publisher=Penguin Reference Library|isbn=0-14-102715-0|year=2006}}
• 6 February – American Revolutionary War: Britain declares war on France for aiding the Americans.{{cite book|last=Palmer|first=Alan|last2=Palmer|first2=Veronica|year=1992|title=The Chronology of British History|publisher=Century Ltd|location=London|pages=227–228|isbn=0-7126-5616-2}}
• 23 April – American Revolutionary War: John Paul Jones in {{USS|Ranger|1777}} raids Whitehaven, with limited effect.
• 24 April – American Revolutionary War: North Channel Naval Duel – John Paul Jones in USS Ranger captures {{HMS|Drake|1777}} in the North Channel.
• May – {{HMS|Victory}} is commissioned and remains in active service for the following 32 years, most notably at the Battle of Trafalgar (1805).{{cite web|url=http://www.icons.org.uk/theicons/icons-timeline/1750-1800|title=Icons, a portrait of England 1750–1800|accessdate=2007-08-25|archiveurl=https://web.archive.org/web/20070817164134/http://www.icons.org.uk/theicons/icons-timeline/1750-1800|archivedate=17 August 2007}}{{cite web|url=http://www.hms-victory.com/index.php?Itemid=104&id=71&option=com_content&task=view|title=HMS Victory|publisher=Royal Navy|accessdate=2010-06-26}}
• 28 May–11 November – American Revolutionary War: In response to the threat of invasion from France, major militia camps are set up at Coxheath Common in Kent and Warley Common near Brentwood, Essex.
• 3 June – Papists Act is the first to provide a measure of Catholic relief.
• 16 June – American Revolutionary War: Spain declares war on Britain.
• 28 June – American Revolutionary War: the Battle of Monmouth in Monmouth, New Jersey, ends inconclusively.{{cite book|last=Williams|first=Hywel|title=Cassell's Chronology of World History|url=https://archive.org/details/cassellschronolo0000will|url-access=registration|location=London|publisher=Weidenfeld & Nicolson|year=2005|isbn=0-304-35730-8|pages=[https://archive.org/details/cassellschronolo0000will/page/331 331–332]}}
• 3 July – American Revolutionary War: the Wyoming Valley battle and massacre takes place near Wilkes-Barre, Pennsylvania, ending in a defeat of the local colonists.
• 10 July – American Revolutionary War: Louis XVI of France declares war on Great Britain.
• 27 July – American Revolutionary War: First Battle of Ushant – British and French fleets fight to a standoff.
• 7 September – American Revolutionary War: French invasion of Dominica captures the British fort there before the latter is aware that France has entered the war in the Franco-American alliance.
• 22 September – first St. Leger Stakes horse race held under this name and at its continuing location, Town Moor, Doncaster.{{cite web|title=Race Courses of Great Britain and Ireland|publisher=tbheritage.com|url=https://www.tbheritage.com/TurfHallmarks/Gazeteer/GazeteerYorks.html|accessdate=2013-01-10}} The winner is Hollandoise.
• 26 November – in the Hawaiian Islands, James Cook becomes the first European to discover Maui.

• Lord Mansfield decides the landmark case of Da Costa v Jones in English contract law, in relation to the presumption of good faith.
• Joseph Bramah invents a type of flush toilet.
• Flint & Clark, the predecessors of Debenhams, begin trading as drapers in London;{{cite web|title=Debenhams Plc History|url=https://www.fundinguniverse.com/company-histories/Debenhams-Plc-Company-History.html|publisher=Funding Universe|year=1999|accessdate=2013-09-04}} their successor will enter liquidation in 2020.
• Fanny Burney's novel Evelina published (anonymously).
• Thomas West's A Guide to the Lakes published.

• American Revolutionary War 1775–1783
• First Anglo-Maratha War 1777–1783

• 1 January – James Grant, major-general (died 1852)
• 4 January – John Manners, 5th Duke of Rutland (died 1857)
• 19 March – Edward Pakenham, general (died 1815)
• 10 April – William Hazlitt, essayist (died 1830)
• 6 May – Henry Phillpotts, Bishop of Exeter (died 1869)
• 18 May
• Charles Vane, 3rd Marquess of Londonderry, politician (died 1854)
• Andrew Ure, doctor and writer (died 1857)
• 7 June – Beau Brummell, arbiter of fashion (died 1840)
• 19 September – Henry Peter Brougham, Lord High Chancellor of Great Britain (died 1868)
• 25 November
• Joseph Lancaster, Quaker educationist (died 1838 in the United States)
• Mary Anne Schimmelpenninck, Christian writer (died 1856)
• 17 December – Humphry Davy, chemist (died 1829)
• 18 December – Joseph Grimaldi, clown (died 1837)

• 5 March – Thomas Augustine Arne, composer (born 1710)
• 22 April – James Hargreaves, weaver, carpenter, and inventor (born 1720)
• 11 May – William Pitt, 1st Earl of Chatham, Prime Minister of Great Britain (born 1708){{cite web |title=History of William Pitt 'The Elder', 1st Earl of Chatham - GOV.UK |url=https://www.gov.uk/government/history/past-prime-ministers/william-pitt-1st-earl-of-chatham |website=www.gov.uk |access-date=20 June 2023 |language=en}}
• 16 May – Robert Darcy, 4th Earl of Holderness, diplomat and politician (born 1718)
• 12 August – Peregrine Bertie, 3rd Duke of Ancaster and Kesteven, general and politician (born 1714)

• 1778 in Wales

{{Reflist}}

• {{citation |title=Annual Register...1778 |location= London |publisher= J. Dodsley |year= 1786 |url= http://catalog.hathitrust.org/Record/008903231 }}

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