1778 in Great Britain

Incumbents

• Monarch – George III
• Prime Minister – Frederick North, Lord North

Events

• 18 January – the third Pacific expedition of James Cook, with ships and, first views Oahu then Kauai in the Hawaiian Islands, which he names the "Sandwich Islands".
• 6 February – American Revolutionary War: Britain declares war on France for aiding the Americans.
• 23 April – American Revolutionary War: John Paul Jones in raids Whitehaven, with limited effect.
• 24 April – American Revolutionary War: North Channel Naval Duel – John Paul Jones in USS Ranger captures in the North Channel.
• May – is commissioned and remains in active service for the following 32 years, most notably at the Battle of Trafalgar.
• 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. Coxheath Camp becomes a fashionable gathering for high society.
• 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.
• 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. The winner is Hollandoise.
• 26 November – in the Hawaiian Islands, James Cook becomes the first European to discover Maui.

Undated

• 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; their successor will enter liquidation in 2020.
• Fanny Burney's novel Evelina published.
• Thomas West's A Guide to the Lakes published.

Ongoing

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

Births

• 1 January – James Grant, major-general
• 4 January – John Manners, 5th Duke of Rutland
• 19 March – Edward Pakenham, general
• 10 April – William Hazlitt, essayist
• 6 May – Henry Phillpotts, Bishop of Exeter
• 18 May
• * Charles Vane, 3rd Marquess of Londonderry, politician
• * Andrew Ure, doctor and writer
• 7 June – Beau Brummell, arbiter of fashion
• 19 September – Henry Peter Brougham, Lord High Chancellor of Great Britain
• 25 November
• * Joseph Lancaster, Quaker educationist
• * Mary Anne Schimmelpenninck, Christian writer
• 17 December – Humphry Davy, chemist
• 18 December – Joseph Grimaldi, clown

Deaths

• 5 March – Thomas Augustine Arne, composer
• 22 April – James Hargreaves, weaver, carpenter, and inventor
• 11 May – William Pitt, 1st Earl of Chatham, Prime Minister of Great Britain
• 16 May – Robert Darcy, 4th Earl of Holderness, diplomat and politician
• 12 August – Peregrine Bertie, 3rd Duke of Ancaster and Kesteven, general and politician