1275 (MCCLXXV) was a common year starting on Tuesday of the Julian calendar, the 1275th year of the Common Era (CE) and Anno Domini (AD) designations, the 275th year of the 2nd millennium, the 75th year of the 13th century, and the 6th year of the 1270s decade. As of the start of 1275, the Gregorian calendar was 7 days ahead of the Julian calendar, which was the dominant calendar of the time.

• April 22 – The first of the Statutes of Westminster are passed by the English parliament, establishing a series of laws in its 51 clauses, including equal treatment of rich and poor, free and fair elections, and definition of bailable and non-bailable offenses.
• Eleanor de Montfort is captured by pirates in the employ of Edward I of England to prevent her marriage to Llywelyn the Last, prince of Wales; she is used as a bargaining chip over the coming years in Edward's attempts to subjugate Llywelyn and Wales.
• Scottish forces defeat the Manx of the Isle of Man in a decisive battle, firmly establishing Scottish rule of the island.
• Third Mongol Golden Horde raid against Lithuania.

• Jean de Meun completes the French allegorical work of fiction, Roman de la Rose, with a second section; the first section was written by Guillaume de Lorris in 1230.
• The verge escapement, a simple type of escapement used in clocks, is invented (exact year unknown).
• Ramon Llull establishes a school in Majorca to teach Arabic to preachers in an attempt to aid proselytizing to Moors. He also discovers diethyl ether.
• The first main survey of the Hundred Rolls, an English census seen as a follow up to the Domesday Book completed in 1086, is finished; it began in 1274.

• March – the 200,000 multiethnic troops of the Mongol-led Yuan Dynasty, headed by the Turkish commander Bayan, face a Chinese Song Dynasty army of 130,000 led by the Song Chancellor Jia Sidao. The result is a decisive victory for the Yuan Dynasty, and soon after the much-vilified Jia Sidao is stripped of rank and title, and killed by one of his own guards as he is sent to exile in Fujian by the Song court.
• Invading Mongol forces capture the Chinese city of Suzhou.
• Marco Polo purportedly visits Xanadu, Kublai Khan's summer capital of the Mongol Empire.
• The city of Kunming is made capital of the Yunnan province of the Mongol Yuan Dynasty.
• Nestorian monk Rabban Bar Sauma begin his pilgrimage from China towards Jerusalem
• Chinese astronomers observe a total eclipse of the Sun in China on March 4.

• The era of the tosafot, Medieval commentators on the Talmud, ends (began 1100).
• The population of Bushmen in Basutoland (modern-day Lesotho) is estimated at 125,000.
• The Japanese era Bun'ei ends, and the Kenji era begins.

• September 27 – John II, Duke of Brabant (died 1312)
• William of Alnwick, Franciscan theologian (approximate date; died 1333)
• Bartholomew de Badlesmere, 1st Lord Badlesmere (died 1322)
• Walter V of Brienne, Duke of Athens (approximate date; died 1311)
• Edward Bruce, Scottish nobleman (approximate date; died 1318)
• Dnyaneshwar, Hindu saint and poet (died 1296)
• Gediminas, Duke of Lithuania (approximate date; died 1341)
• Henry VII, Holy Roman Emperor (approximate date; died 1313)
• Mondino de Liuzzi, Italian physician and anatomist (died 1326)
• John Menteith, Scottish nobleman (approximate date; died 1323)
• Giovanni Villani, Florentine writer (approximate date; died 1348)
• Giovanni d'Andrea, Italian jurist

• April 13 – Eleanor of England (born 1215)
• September 24 – Humphrey de Bohun, 2nd Earl of Hereford, Constable of England (born 1208)
• Bohemund VI of Antioch (born 1237)
• Ferdinand de la Cerda, Infante of Castile, Crown Prince of Castile