|Covid-19|January 5 – The United States House of Representatives votes to stop sharing the Oregon Country with the United Kingdom.
January 13 – Opening of the Milan–Venice railway's 3.2 km (2.0 mi) bridge over the Venetian Lagoon between Mestre and Venice in Italy, 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: British victory at the Battle of Sobraon.
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 – Beginning of the Galician peasant revolt.
February 19 – The newly formed Texas state government is officially installed in Austin.
February 20 –29 – Kraków Uprising: Polish nationalists stage an uprising in the Free City of Kraków, suppressed by forces of the Austrian Empire supported by peasants in the Galician slaughter.
February 26 – The Liberty Bell is cracked while being rung for George Washington's birthday.
March 9 – The conclusion of the First Anglo-Sikh War 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 border disputes of Texas' boundaries.
May – Associated Press 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 was founded by future United States President and Vice 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 – Revolution of Maria da Fonte in Portugal (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.
The Oregon Treaty establishes the 49th parallel as the border between the United States and Canada, from the Rocky Mountains to the Strait of Juan de Fuca.
Launceston Church Grammar School opens for the first time in Tasmania.
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 – 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 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 the British astronomer John Couch Adams and the French astronomer Urbain Le Verrier.
October 1 – Christ College, Tasmania, opens with the hope that it would 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 anasthesia.
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 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.
Cholera epidemic in England.
Great Famine continues in Ireland.
Mariam Baouardy, Syrian Melkite Greek Catholic nun, canonized (d. 1878)
Rudolf Christoph Eucken, German writer, Nobel Prize laureate (d. 1926)
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 (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 and 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)
June 11 – William Louis Marshall, American general and 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, the 14th shogun of the Tokugawa shogunate of Japanese (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)
Watson Heston, American cartoonist (d. 1905)
Wladimir Köppen, Russian-German geographer and climatologist (d. 1940)
October 6 – George Westinghouse, American entrepreneur and engineer (d. 1914)
October 26 – Lewis Boss, American astronomer (d. 1912)
November 10 – Martin Wegelius, Finnish composer and musicologist (d. 1906)
November 13 – Herbert Standing, English actor (d. 1923)
November 25 – Carrie Nation, American temperance advocate (d. 1911)
December 17 – Max von Hausen, German general (d. 1922)
December 21 – Julia Lermontova, Russian chemist (d. 1919)
Konstantinos Koumoundouros, Greek army officer and politician (d. 1924)
Jeanne Schmahl, British-born French feminist (d. 1915)
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)
Samuel Humphreys, American naval architect (b. 1778)
Sylvain Charles Valée, Marshal of France (b. 1773)
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)
Alexander Chavchavadze, Georgian Romantic poet and military figure (b. 1786)
Karol Marcinkowski, Polish physician and social activist (b. 1800)
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)
date unknown – Maria Medina Coeli, Italian physician (b. 1764)
1846 (MDCCCXLVI) was a common year starting on Thursday (dominical letter D) of the Gregorian calendar and a common year starting on Tuesday (dominical letter F) 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.