October 25 is the 298th day of the year (299th in leap years) in the Gregorian calendar. There are 67 days remaining until the end of the year.

• 1147 – The Portuguese, under Afonso I, and Crusaders from England and Flanders conquer Lisbon after a four-month siege.
• 1147 – Seljuk Turks completely annihilate German crusaders under Conrad III at the Battle of Dorylaeum.
• 1415 – The army of Henry V of England defeats the French at the Battle of Agincourt.
• 1616 – Dutch sea-captain Dirk Hartog makes second recorded landfall by a European on Australian soil, at the later-named Dirk Hartog Island off the West Australian coast.
• 1747 – British fleet under Admiral Sir Edward Hawke defeats the French at the second battle of Cape Finisterre.
• 1760 – George III becomes King of Great Britain.
• 1812 – War of 1812: The American heavy frigate, USS United States, commanded by Stephen Decatur, captures the British frigate HMS Macedonian.
• 1828 – The St Katharine Docks opened in London.
• 1854 – The Battle of Balaklava during the Crimean War (Charge of the Light Brigade).
• 1861 – The Toronto Stock Exchange is created.
• 1900 – The United Kingdom annexes the Transvaal.
• 1917 – Traditionally understood date of the October Revolution, involving the capture of the Winter Palace, Petrograd, Russia. The date refers to the Julian Calendar date, and corresponds with November 7 in the Gregorian calendar.
• 1920 – After 74 days on Hunger Strike in Brixton Prison, England, the Sinn Féin Lord Mayor of Cork, Terence MacSwiney died.
• 1924 – The forged Zinoviev Letter is published in the Daily Mail, wrecking the British Labour Party's hopes of re-election.
• 1938 – The Archbishop of Dubuque, Francis J. L. Beckman, denounces swing music as "a degenerated musical system... turned loose to gnaw away at the moral fiber of young people", warning that it leads down a "primrose path to hell".
• 1940 – Benjamin O. Davis, Sr. is named the first African American general in the United States Army.
• 1944 – Heinrich Himmler orders a crackdown on the Edelweiss Pirates, a loosely organized youth culture in Nazi Germany that had assisted army deserters and others to hide from the Third Reich.
• 1944 – The USS Tang under Richard O'Kane (the top American submarine captain of World War II) is sunk by the ship's own malfunctioning torpedo.
• 1944 – The Romanian Army liberates Carei, the last Romanian city under Axis Powers occupation.
• 1944 – Battle of Leyte Gulf, the largest naval battle in history, takes place in and around the Philippines between the Imperial Japanese Navy and the U.S. Third and U.S. Seventh Fleets.
• 1945 – The Republic of China takes over administration of Taiwan following Japan's surrender to the Allies.
• 1962 – Cuban missile crisis: Adlai Stevenson shows photos at the UN proving Soviet missiles are installed in Cuba.
• 1962 – Uganda joins the United Nations.
• 1962 – Nelson Mandela is sentenced to five years in prison.
• 1971 – The United Nations seated the People's Republic of China and expelled the Republic of China (see political status of Taiwan and China and the United Nations)
• 1977 – Digital Equipment Corporation releases OpenVMS V1.0.
• 1980 – Proceedings on the Hague Convention on the Civil Aspects of International Child Abduction conclude at The Hague.
• 1983 – Operation Urgent Fury: The United States and its Caribbean allies invade Grenada, six days after Prime Minister Maurice Bishop and several of his supporters are executed in a coup d'état.
• 1991 – History of Slovenia: Three months after the end of the Ten-Day War, the last soldier of the Yugoslav People's Army leaves the territory of the Republic of Slovenia.
• 1995 – A commuter train slams into a school bus in Fox River Grove, Illinois, killing seven students.
• 1997 – After a brief civil war which has driven President Pascal Lissouba out of Brazzaville, Denis Sassou-Nguesso proclaims himself the President of the Republic of the Congo.
• 2004 – Fidel Castro, Cuba's President, announces that transactions using the American Dollar will be banned.
• 2009 – The 25 October 2009 Baghdad bombings kills 155 and wounds at least 721.