1846 (MDCCCXLVI) was a common year starting on Thursday of the Gregorian calendar and a common year starting on Tuesday of the Julian calendar, the 1846th year of the Common Era (CE) and Anno Domini (AD) designations, the 846th year of the 2nd millennium, the 46th year of the 19th century, and the 7th year of the 1840s decade. As of the start of 1846, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.
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- January 5 – The United States House of Representatives votes to stop sharing the Oregon Country with the United Kingdom.
- The Milan–Venice railway's 3.2 km (2.0 mi) bridge, over the Venetian Lagoon between Mestre and Venice in Italy, opens, the world's longest since 1151.
- Many Mormons begin their migration west from Nauvoo, Illinois, to the Great Salt Lake, led by Brigham Young.
- First Anglo-Sikh War – Battle of Sobraon: British forces defeat the Sikhs.
- February 14 – United States president James K. Polk annexes the Republic of Texas, which is regarded as an early example of American imperialism.
- February 18 – The Galician peasant revolt begins.
- February 19 – The newly formed Texas state government is officially installed in Austin.
- February 20 –29 – Kraków Uprising – Galician slaughter: Polish nationalists stage an uprising in the Free City of Kraków; it is suppressed by forces of the Austrian Empire, supported by peasants.
- February 26 – The Liberty Bell is cracked, while being rung for George Washington's birthday.
- March 9 – The First Anglo-Sikh War ends, with the signing of the Treaty of Lahore. Kashmir is ceded to the British East India Company, and the Koh-i-Noor diamond is surrendered to Queen Victoria.
- March 10 – Prince Osahito, fourth son of deceased Emperor Ninkō of Japan, becomes Emperor Kōmei.
- April 25 – Mexican–American War: Open conflict begins, over the disputed border of Texas.
- May – The Associated Press is founded in New York.
- May 8 – Mexican–American War – Battle of Palo Alto: Zachary Taylor defeats a Mexican force north of the Rio Grande at Palo Alto, Texas in the first major battle of the war.
- May 11 – The University at Buffalo is founded by future United States Vice President and President, Millard Fillmore.
- May 13 – Mexican–American War: The United States declares war on Mexico.
- May 15 – Under the leadership of Prime Minister Robert Peel, the House of Commons of the United Kingdom votes to repeal the Corn Laws by passing an Importation Bill, replacing the old colonial mercantile trade system with free trade. On June 25 the Duke of Wellington persuades the House of Lords to pass the Act, which will take full effect from February 1849.
- May 16 – The Revolution of Maria da Fonte begins in Portugal (it is crushed by royalist troops on February 22, 1847).
- May 25 – The Royal Geographical Society awards Paweł Edmund Strzelecki a Gold Medal "for exploration in the south eastern portion of Australia".
- June 10 – Mexican–American War: The California Republic declares independence from Mexico.
- June 14 – Bear Flag Revolt: American settlers in Sonoma, California, start a rebellion against Mexico and proclaim the California Republic.
- June 15
- June 16 – Pope Pius IX succeeds Pope Gregory XVI as the 255th pope. He will reign for 31½ years (the longest definitely confirmed).
- June 28 – The saxophone is patented by Adolphe Sax.
- July 7 – Mexican–American War – Battle of Monterey: Acting on instructions from Washington, D.C., Commodore John Drake Sloat orders his troops to occupy Monterey and Yerba Buena, thus beginning the United States annexation of California.
- August 22 – The Second Federal Republic of Mexico is established.
- September – The Second Carlist War (or the War of the Matiners or Madrugadores) begins in Spain.
- September 10 – Elias Howe is awarded the first United States patent for a sewing machine, using a lockstitch design.
- September 12 – Elizabeth Barrett elopes with Robert Browning.
- September 14 – Jang Bahadur and his brothers massacre about 40 members of the Nepalese palace court.
- September 19 – The Virgin Mary is said to have appeared to two children in La Salette, France.
- September 23 – Discovery of Neptune: The planet is observed for the first time by German astronomers Johann Gottfried Galle and Heinrich Louis d'Arrest, as predicted by British astronomer John Couch Adams and French astronomer Urbain Le Verrier.
- October 1 – Christ College, Tasmania, opens with the hope that it will develop along the lines of an Oxbridge college, and provide the basis for university education in Tasmania. By the 21st century it will be the oldest tertiary institution in Australia.
- October 16 – At Massachusetts General Hospital, Dr. William T.G. Morton, a dentist, gives the first successful public demonstration of ether anesthesia. 
- November 4 – The Donner Party, a wagon train of 87 settlers traveling to California, is stranded in the Sierra Nevada mountains by the first of several snowstorms. By the time a relief party reaches the starving settlers three months later, only 48 survivors are left, many of whom have survived by cannibalism. 
- Pope Pius IX issues the encyclical Qui pluribus, in response to the growing trend of agnosticism among intellectuals in Europe. 
- December 22 – The Guildsystem in Sweden is abolished by the Fabriks och Handtwerksordning and Handelsordningen, and trade and handicrafts permits are granted to every male and female applicant of legal majority.
- December 24 – Great Britain acquires Labuan from the Sultanate of Brunei.
- December 28 – Iowa is admitted as the 29th U.S. state.
- The portion of the District of Columbia, that was ceded by Virginia in 1790, is re-ceded to Virginia.
- Electric Telegraph Company founded in Britain.
- Abraham Pineo Gesner develops a process to refine a liquid fuel, which he calls kerosene, from coal, bitumen or oil shale.
- Fort Wayne Female College is founded; it will later be renamed Taylor University.
- A cholera epidemic breaks out in England.
- The Great Famine continues in Ireland.
- January 5
- January 27 – M. Lewis Clark American founder of Kentucky Derby (d. 1899)
- February 2 – Francis Marion Smith, American borax magnate (d. 1931)
- February 9 – Wilhelm Maybach, German automobile designer (d. 1929)
- February 18 – Wilson Barrett, English actor (d. 1904)
- February 21 – James Timberlake, American lawman (d. 1891)
- February 26 – William F. "Buffalo Bill" Cody, American frontiersman, later showman (d. 1917)
- March 4 – Franklin J. Drake, American admiral (d. 1929)
- March 6 – Henry Radcliffe Crocker, English dermatologist (d. 1909)
- March 9 – Ōdera Yasuzumi, Japanese general (d. 1895)
- March 24 – Karl von Bülow, German field marshal (d. 1921)
- April 4 – Comte de Lautréamont, French writer (d. 1870)
- May 3 – Sir Edmund Elton, 8th Baronet, English inventor, studio potter (d. 1920)
- May 5 – Henryk Sienkiewicz, Polish author, Nobel Prize laureate (d. 1916)
- May 20 – Alexander von Kluck, German general (d. 1934)
- May 22 – Rita Cetina Gutiérrez, American teacher, poet, and activist (d. 1908)
- May 25 – Princess Helena of the United Kingdom (d. 1923)
- May 29 – Winfield Scott Edgerly, United States Brigadier General (d. 1927)
- June 11 – William Louis Marshall, American general, engineer (d. 1920)
- June 13 – Rose Cleveland, de facto First Lady of the United States (d. 1918)
- June 27 – Charles Stewart Parnell, Irish political leader (d. 1891)
- July 17 – Tokugawa Iemochi, 14th shōgun of the Tokugawa shogunate of Japan (d. 1866)
- July 26 – Texas Jack Omohundro, American frontier scout, actor, and cowboy (d. 1880)
- July 29 – Isabel, Princess Imperial of Brazil (d. 1921)
- August 16 – Oskar Victorovich Stark, Russian admiral and explorer (d. 1928)
- August 18 – Robley Dunglison Evans, American admiral (d. 1912)
- August 23 – Alexander Milne Calder, American sculptor (d. 1923)
- September 7 – John Porter Merrell, American admiral (d. 1916)
- September 16 – Anna Kingsford, British spiritual writer, doctor, feminist and pioneering vegetarian (d. 1888)
- September 21 – Mihály Kolossa, Hungarian Slovene writer (d. 1906)
- September 25
- October 6 – George Westinghouse, American entrepreneur, engineer (d. 1914)
- October 26 – Lewis Boss, American astronomer (d. 1912)
- November 10 – Martin Wegelius, Finnish composer, musicologist (d. 1906)
- November 13 – Herbert Standing, English actor (d. 1923)
- November 20 – Konstantinos Koumoundouros, Greek army officer, politician (d. 1924)
- November 25 – Carrie Nation, American temperance advocate (d. 1911)
- December 2 – Pierre Waldeck-Rousseau, Prime Minister of France (d. 1904)
- December 17 – Max von Hausen, German general (d. 1922)
- December 21 – Julia Lermontova, Russian chemist (d. 1919)
- February 21 – Emperor Ninkō of Japan (b. 1800)
- February 27 – María Trinidad Sánchez, heroine of the Dominican War of Independence (b. 1794)
- March 17 – Friedrich Bessel, German mathematician and astronomer (b. 1784)
- May 11 – Jane Irwin Harrison, de facto First Lady of the United States (b. 1804)
- May 23 – Franciszek Ksawery Drucki-Lubecki, Polish politician (b. 1778)
- June 1 – Pope Gregory XVI (b. 1765)
- June 8 – Rodolphe Töpffer, Swiss author, painter, and caricature artist (b. 1799)
- June 13 – Jean-Baptiste Benoît Eyriès, French geographer, author and translator (b. 1767)
- August 16
- September 14 – Jacques Dupré, Louisiana State Representative, State Senator, and Governor (b. 1773)
- September 23 – John Ainsworth Horrocks, English-born explorer of South Australia (b. 1818)
- September 26 – Thomas Clarkson, English abolitionist (b. 1760)
- November 6
- November 12 – William Findlay, American politician (b. 1768)
- December 18 – Emilie Högquist, Swedish dramatic star (b. 1812)
- December 29 – Mateli Magdalena Kuivalatar, Finnish-Carelian folksinger (b. 1777)
- "Venice Railroad Bridge". Structurae. Retrieved 2012-02-22.
- Kalla-Bishop, P. M. (1971). Italian Railways. Newton Abbot: David & Charles. p. 20. ISBN 0-7153-5168-0.
- Palmer, Alan; Veronica (1992). The Chronology of British History. London: Century Ltd. pp. 268–269. ISBN 0-7126-5616-2.
- Penguin Pocket On This Day. Penguin Reference Library. 2006. ISBN 0-14-102715-0.
- "Chancellors and Presidents of the University". University of Buffalo, The State University of New York. Retrieved 2016-12-06.
- "Icons, a portrait of England 1840–1860". Archived from the original on August 17, 2007. Retrieved 2007-09-13.
- Hart, Hugh (2010-06-28). "June 28, 1846: Parisian Inventor Patents Saxophone". Wired. Retrieved 2011-12-07.
- U.S. Patent 4,750
- Lilian R. Furst, Medical Progress and Social Reality: A Reader in Nineteenth-Century Medicine and Literature (SUNY Press, 2000) p16
- George R. Stewart, Ordeal by Hunger: The Story of the Donner Party (Houghton Mifflin Harcourt, 2013) pp366-367
- Gerald A. McCool, Nineteenth-century Scholasticism: The Search for a Unitary Method (Fordham University Press, 1989) p129
- Du Rietz, Anita, Kvinnors entreprenörskap: under 400 år, 1. uppl., Dialogos, Stockholm, 2013, s 270