The Toluid Civil War ends. Kublai Khan defeats his brother and pretender to the title of Khagan, or Khan of Khans, Ariq Boke, who surrenders to Kublai and is summarily imprisoned. He dies a year later under mysterious circumstances, possibly by poisoning, but the cause of death is still uncertain. However, this battle essentially marks the end of a unified Mongol Empire.
Kublai Khan decides to move his capital from Shangdu in Inner Mongolia to the Chinese city of Dadu (now Beijing).
Kublai Khan publicly reprimands his own officers for executing 2 Song Dynasty Chinese generals without trial or investigation. This act is one of many in order to enhance his reputation amongst the Chinese, to increase his legitimacy as a just ruler, and win over more defectors from the Southern Song.
The Japanese era Kōchō ends, and the Bun'ei era begins.
January 23 – King Louis IX of France issues the Mise of Amiens, a settlement between King Henry III of England and barons led by Simon de Montfort heavily favouring the former, which leads to the Second Barons' War.
April – Gilbert de Clare, 6th Earl of Hertford leads a massacre of the Jews at Canterbury.
Before May – The Second Barons' War, a civil war in England, begins.
May 12–May 14 – The Battle of Lewes of the Second Barons' War is fought between Simon de Montfort, 6th Earl of Leicester and King Henry III of England in Sussex. By the end of the battle, de Montfort's forces capture both King Henry and his son, future King Edward I, making de Montfort the "uncrowned king of England" for 15 months before Edward escapes captivity and recaptures the throne.
June 18 – The Parliament of Ireland meets at Castledermot in County Kildare, the first definitively known meeting of this Irish legislature.
August 5 – Anti-Jewish riots break out in Arnstadt (modern-day Germany).
In Spain, King James I of Aragon reconquers the cities of Orihuela in Alicante and Elx in Valencia from the Moors, ending over 500 years of Islamic rule.
October 9 – King Alfonso X "the Wise" recapture the town of Jerez de la Frontera in Spain from the Muslims.
The War of the Thuringian Succession ends.
The state of Hesse gains its independence from Thuringia and becomes a free state of the Holy Roman Empire.
In the Peerage of England, the title Baron de Ros, the oldest continuously held peerage title in England, is created by writ of summons.
Sinucello della Rocca becomes lord of Corsica and rules the island, benefiting from the rivalry of Pisa and Genoa.
King Boleslaus V of Poland promulgates legal protection for his Jewish subjects, including protection from the kidnapping and forcible baptism of Jewish children.
September 14 – Walter de Merton formally completes the foundation of the House of Scholars of Merton (later Merton College, Oxford) to provide education in Malden and the University of Oxford.
In Barcelona, a commission of Dominicans censors portions of the Talmud for the first time, by ordering the cancellation of passages found reprehensible from a Christian point of view.
Thomas Aquinas completes his theological work Summa contra Gentiles (traditional dating).
Pope Urban IV creates the festivity of Corpus Domini.
May 26 – Prince Koreyasu, Japanese shogun (d. 1326)
Pope Clement V (d. 1314)
April 25 – Roger de Quincy, 2nd Earl of Winchester, English politician (b. 1195)
October 2 – Pope Urban IV
John II of Beirut
Vincent of Beauvais, French encyclopedist (b. 1190)
Danylo of Halych, King of Galicia (b. 1201)
Emperor Lizong of China
Andrei II of Russia, Grand Prince of Vladimir
Year 1264 (MCCLXIV) was a leap year starting on Tuesday (link will display the full calendar) of the Julian calendar.