1788

January–March

• January 1 – The first edition of The Times, previously The Daily Universal Register, is published in London.
• January 2 – Georgia ratifies the United States Constitution, and becomes the fourth U.S. state under the new government.
• January 9 – Connecticut ratifies the United States Constitution, and becomes the fifth U.S. state.
• January 18 – The leading ship in Captain Arthur Phillip's First Fleet arrives at Botany Bay, to colonise Australia.
• January 22 – The Congress of the Confederation, effectively a caretaker government until the United States Constitution can be ratified by at least nine of the 13 states, elects Cyrus Griffin as its last president.
• January 24 – The La Perouse expedition in the Astrolabe and Boussole arrives off Botany Bay, just as Captain Arthur Phillip is attempting to move his colony from there to Sydney Cove in Port Jackson.
• January 26 – Eleven ships of the First Fleet from Botany Bay, led by Captain Arthur Phillip, land at Sydney Cove, Australia, where he determines to establish the British prison colony of New South Wales, the first permanent European settlement on the continent.
• January 31 – Henry Benedict Stuart becomes the new Stuart claimant to the throne of Great Britain, as King Henry IX and the figurehead of Jacobitism.
• February 1 – Isaac Briggs and William Longstreet patent a steamboat.
• February 6 – Massachusetts ratifies the United States Constitution, and becomes the sixth U.S. state.
• February 7 – Sydney is named and founded, in the British colony of New South Wales.
• February 9 – Austria enters the Russo-Turkish War (1787–92), and attacks Moldavia.
• February 17 – The uninhabited Lord Howe Island is discovered by the brig HMS Supply, commanded by Lieutenant Ball, who is on his way from Botany Bay to Norfolk Island with convicts to start a penal settlement there. They arrive at Norfolk Island on March 6.
• March 10 – The La Perouse expedition leaves Sydney Cove for New Caledonia, never to be seen again.
• March 14 – The Edinburgh Evening Courant carries a notice of £200 reward for the capture of William Brodie, a town councilor doubling as a burglar.
• March 21 – The Great New Orleans Fire destroys 856 buildings, including St. Louis Cathedral and The Cabildo, leaving most of the town in ruins.

April–June

• April 7 – American pioneers establish the town of Marietta, the first permanent American settlement outside the original Thirteen Colonies.
• April 13 – America's first recorded riot, the 'Doctors' Mob', begins. Residents of Manhattan are angry about grave robbers stealing bodies for doctors to dissect. The rioting is suppressed on April 15.
• April 28 – Maryland ratifies the United States Constitution, and becomes the seventh U.S. state.
• May 10 – The Royal Dramatic Theatre, Sweden's national drama company, is founded.
• May 15 – The Australian frontier wars begins. With the placement of a cournerstone.
• May 23 – South Carolina ratifies the United States Constitution, and becomes the eighth U.S. state.
• June 7 – France: Day of the Tiles, which some consider the beginning of the French Revolution.
• June 9 – The African Association, an exploration group dedicated to plotting the Niger River and finding Timbuktu, is founded in England.
• June 17 – English captains Thomas Gilbert and John Marshall, returning from Botany Bay, become the first Europeans to encounter the Gilbert Islands in the Pacific Ocean. They also chart islands in "Lord Mulgrove's range", later known as the Marshall Islands.
• June 21 – New Hampshire ratifies the United States Constitution, and becomes the ninth U.S. state, enabling the Constitution to go into effect.
• June 25 – The Virginia Ratifying Convention ratifies the United States Constitution, and becomes the tenth U.S. state under the new government.
• June 26 – Wolfgang Amadeus Mozart, in Vienna, completes his antepenultimate symphony, now called the Symphony No. 39 in E-flat.
• June 27 – The Russo-Swedish War (1788–1790) breaks out following a staged attack on Swedish troops in Puumala, present-day Finland.

July–September

• July 13 – A hailstorm sweeps across France and the Dutch Republic, with hailstones 'as big as quart bottles' that take 'three days to melt'; immense damage is done.
• July 24 – Governor General Lord Dorchester, by proclamation issued from the Chateau St. Louis in Quebec City, divides the British Province of Quebec into five Districts, namely: Gaspé, Nassau, Lunenburg, Mecklenburg, and Hesse.
• July 26 – New York ratifies the United States Constitution, and becomes the eleventh U.S. state.
• July 28 – Wolfgang Amadeus Mozart, in Vienna, completes his penultimate symphony, now called the Symphony No. 40 in G Minor.
• August 8 – King Louis XVI agrees to convene the Estates-General meeting in May 1789, the first time since 1614.
• August 10 – Emperor Shah Alam II was blinded by a maddened Indo-Afghan commander Ghulam Qadir Rohilla who sought revenge against the Mughal Empire.
• August 10 – Wolfgang Amadeus Mozart, in Vienna, completes his final symphony, now called the Symphony No. 41 in C Major, and nicknamed The Jupiter.
• August 12 – The Anjala conspiracy is signed.
• August 27 – The trial of Deacon William Brodie for burglary begins in Edinburgh, Scotland; he is sentenced to death by hanging.
• September 13 – The United States Congress of the Confederation passes an act providing a timeline for the voting for the first President under the new U.S. Constitution.
• September 21 – Austro-Turkish War - Battle of Karánsebes: The Austrian army engages in a friendly-fire incident, which results in mass casualties.
• September 24 – The Theater War begins, when the army of Denmark–Norway invades Sweden.

October–December

• October 1 – William Brodie is hanged at the Tolbooth in Edinburgh.
• October 21 – The 14th and last session of the Continental Congress and is adjourned.
• October – King George III of the United Kingdom becomes deranged; the Regency Crisis of 1788 starts.
• November 8 – Voting takes place in the 11 states that have ratified the United States Constitution for the first U.S. Senators; in Virginia, Richard Henry Lee and William Grayson, both anti-federalists, receive the highest number of votes in the Virginia Senate.
• November 15 – Cyrus Griffin of Virginia completes his service as the last President of the Congress of the Confederation, under the Articles of Confederation.
• November 20 – In the United Kingdom, the Houses of Parliament are given the first formal report by Prime Minister Pitt of the mental illness of King George III. Parliament adjourns for two weeks, to await the results of examinations by royal physicians.
• November 25 – Fifty consecutive days of temperatures below freezing strike France, a record that will be unbroken more than 200 years later.
• December 6 – Russo-Turkish War (1787–92): The Ottoman fortress of Ochakiv falls to the Russians after a prolonged siege, and a murderous storm with a temperature of.
• December 14 – King Charles III of Spain dies, and is succeeded by his son Charles IV.
• December – Robert Burns writes his version of the Scots poem Auld Lang Syne.

Undated

• Annual British iron production reaches 68,000 tons.