1831 (MDCCCXXXI) was a common year starting on Saturday (dominical letter B) of the Gregorian calendar and a common year starting on Thursday (dominical letter D) of the Julian calendar, the 1831st year of the Common Era (CE) and Anno Domini (AD) designations, the 831st year of the 2nd millennium, the thirty-first year of the 19th century, and the second year of the 1830s decade. Note that the Julian day for 1831 is 12 calendar days difference, which continued to be used from 1582 until the complete conversion of the Gregorian calendar was entirely done in 1929.
- January 1 – William Lloyd Garrison begins publishing The Liberator, an antislavery newspaper, in Boston, Massachusetts.
- January 14 – The Hunchback of Notre-Dame is first published by Victor Hugo.
- February–March – Revolts in Modena, Parma and the Papal States are put down by Austrian troops.
- February 2 – Pope Gregory XVI succeeds Pope Pius VIII as the 254th pope.
- February 7 – Belgian Constitution of 1831 approved by the National Congress
- February 14 – Battle of Debre Abbay: Ras Marye of Yejju marches into Tigray and defeats and kills the warlord Sabagadis.
- February 20 – Battle of Olszynka Grochowska (Grochow): Polish rebel forces divide a Russian army.
- March 10 – The French Foreign Legion is founded.
- March 29 – The Bosnian Uprising against the Ottoman Empire begins.
- April 7 – Pedro I abdicates as Emperor of Brazil in favour of his 5-year-old son Pedro II, who'll reign for almost 59 years.
- April 18 – University of Alabama founded.
- April 27 – Charles Albert becomes king of Sardinia after the death of King Charles Felix.
- May 26 – Battle of Ostrołęka: The Poles fight another indecisive battle.
- May–June – Merthyr Rising: Coal miners and others riot in Merthyr Tydfil, Wales for improved working conditions.
- June 1 – British Royal Navy officer James Clark Ross locates the position of the North Magnetic Pole on the Boothia Peninsula.
- c.July 15 – The volcanic island of Graham Island briefly emerges in the Mediterranean.
- July 21 – Leopold of Saxe-Coburg-Gotha is inaugurated as first King of the Belgians in Brussels.
- August 2 – The Dutch Ten Days' Campaign against Belgium is halted by a French army.
- August 7 – American Baptist minister William Miller preaches his first sermon on the Second Advent of Christ in Dresden, New York, launching the Advent Movement in the United States.
- August 21 – United States: Nat Turner's slave rebellion breaks out in Southampton County, Virginia.
- September 6–September 8 – Battle of Warsaw: The Russians take the Polish capital and crush resistance.
- September 8 – The coronation of King William IV of the United Kingdom who succeeded his brother George IV. He would reign until 1837
- November 7 – Slave trading is forbidden in Brazil.
- November 22 – After a bloody battle with the military causing 600 casualties, rebellious silk workers seize Lyon, France, beginning the First Canut Revolt.
- December 27 – Charles Darwin embarks on his historic voyage aboard HMS Beagle.
- December 31 – Gramercy Park is deeded to New York City.
- The Sydney Morning Herald newspaper is first published.
- Muhammad Ali of Egypt's French-trained forces occupy Syria.
- Rifa'a al-Tahtawi returns from study in Paris to Egypt.
- Founding of:
- January 3 – Savitribai Jyotirao Phule an Indian social reformer and poet (d. 1897)
- January 7 – Heinrich von Stephan, German postal union organiser (d. 1897)
- February 24 – Leo von Caprivi, Chancellor of Germany (d. 1899)
- March 3 – George Pullman, American inventor and industrialist (d. 1897)
- March 6 – Philip Sheridan, American general (d. 1888)
- March 12 – Clement Studebaker, American automobile pioneer (d. 1901)
- March 16 – Elise Hwasser, Swedish artist (d. 1894)
- March 20 – Solomon L. Spink, U.S. Congressman from Illinois (d. 1881)
- June 1 – John Bell Hood, American Confederate general (d. 1879)
- June 2 – Jan Gerard Palm, composer (d. 1906)
- June 13 – James Clerk Maxwell, Scottish physicist (d. 1879)
- June 28 – Joseph Joachim, Austrian violinist (d. 1907)
- July 8 – John Pemberton, inventor of Coca-Cola (d. 1888)
- July 17 – Xianfeng Emperor of China (d. 1861)
- July 22 – Emperor Kōmei of Japan (d. 1867)
- August 12 – Helena Blavatsky, Russian-born author and theosophist (d. 1891)
- August 20 – Eduard Suess, Austrian geologist (d. 1914)
- September 8 – Wilhelm Raabe, German novelist (d. 1910)
- September 18 – Siegfried Marcus, German-born automobile pioneer (d. 1898)
- September 20 – Kate Harrington, American teacher, writer and poet (d. 1917)
- September 29 – John Schofield, American general (d. 1906)
- October 6 – Richard Dedekind, German mathematician (d. 1916)
- October 16 – Lucy Stanton, American abolitionist (d. 1910)
- October 18 – Frederick III, German Emperor (d. 1888)
- October 29 – Othniel Charles Marsh, American palaeontologist (d. 1899)
- October 31 – Romualdo Pacheco, Governor of California (d. 1899)
- November 5 – Anna Leonowens, Anna of The King and I (d. 1915)
- November 19 – James A. Garfield, twentieth United States President (d. 1881)
- December 19 – Bernice Pauahi Bishop, Hawaiian aliʻi (d. 1884)
- Sotirios Sotiropoulos, Greek economist and politician (d. 1898)
- Eugenia Kisimova, Bulgarian feminist, philanthropist and women's rights activist (d. 1885)
- January 8 – Franz Krommer, Czech composer (b. 1759)
- January 21 – Ludwig Achim von Arnim, German poet (b. 1781)
- February 14
- February 17 – Friedrich Wilhelm, Duke of Schleswig-Holstein-Sonderburg-Glücksburg (b. 1785)
- February 25 – Friedrich Maximilian Klinger, German writer (b. 1752)
- April 5 – Dmitry Senyavin, Russian admiral (b. 1763)
- April 20 – John Abernethy, English surgeon (b. 1764)
- April 27 – Charles Felix of Sardinia, King of Sardinia (b. 1765)
- April 30 – Collet Barker, British military officer and explorer (b. 1784)
- June 8 – Sarah Siddons, English actress (b. 1755)
- June 27 – Sophie Germain, French mathematician (b. 1776)
- July 4 – James Monroe, fifth President of the United States (b. 1758)
- July 16 – Louis Alexandre Andrault de Langeron, Russian general (b. 1763)
- August 24 – August von Gneisenau, Prussian field marshal (b. 1760)
- November 11 – Nat Turner, American slave rebel (b. 1800)
- November 14 – Georg Hegel, German philosopher (b. 1770)
- November 16 – Carl von Clausewitz, German military strategist (b. 1780)
- December 26 – Henry Louis Vivian Derozio, Indian poet (b. 1809)
Marengo, Napoleon's mount in several battles (b. 1793)