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1859 (MDCCCLIX) was a common year starting on Saturday of the Gregorian calendar and a common year starting on Thursday of the Julian calendar, the 1859th year of the Common Era (CE) and Anno Domini (AD) designations, the 859th year of the 2nd millennium, the 59th year of the 19th century, and the 10th and last year of the 1850s decade. As of the start of 1859, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.
- January 24 (O. S.) – Wallachia and Moldavia are united under Alexandru Ioan Cuza (Romania since 1866, final unification takes place on December 1, 1918; Transylvania and other regions are still missing at that time).
- January 28 – The city of Olympia is incorporated in the Washington Territory, in the United States of America.
- February 4 – German scholar Constantin von Tischendorf rediscovers the Codex Sinaiticus, a 4th-century uncial manuscript of the Greek Bible, in Saint Catherine's Monastery on the foot of Mount Sinai, in the Khedivate of Egypt.
- February 14 – Oregon is admitted as the 33rd U.S. state.
- February 17 – French naval forces under Charles Rigault de Genouilly capture the city and Citadel of Saigon in Vietnam, beginning the Siege of Saigon.
- February 27 – United States Congressman Daniel Sickles shoots Philip Barton Key (U.S. District Attorney), for having an affair with his wife.
- March 9 – The army of the Kingdom of Sardinia mobilizes against Austria, beginning the crisis which will lead to the Austro-Sardinian War.
- March 21 – The Commonwealth of Pennsylvania issues the charter establishing the Zoological Society of Philadelphia, the first organization of its kind in the United States, and founder of the nation's first zoo.
- March 26 – A French amateur astronomer, Edmond Modeste Lescarbault, claims to have noticed a planet closer to the Sun than Mercury (later named Vulcan).
- April 13 – The Cooper Union for the Advancement of Science and Art is founded by Peter Cooper, a New York industrialist, inventor and philanthropist.
- April 25 – Ground is broken for the Suez Canal, in Egypt.
- April 28 – The Pomona is wrecked off the English coast, with 424 dead.
- April 29 – Austrian troops begin to cross the Ticino River to Piedmont.
- April 30 – A Tale of Two Cities by Charles Dickens is published in England.
- May 4 – The Cornwall Railway opens across the Royal Albert Bridge, linking the counties of Devon and Cornwall in England.
- May 5 – Border Treaty between Brazil and Venezuela: The two countries agree their borders should be traced at the water divide, between the Amazon and the Orinoco basins.
- May 22 – Ferdinand II of the Two Sicilies is succeeded by his 23-year-old son, Francis II of the Two Sicilies.
- May 26 – Austro-Sardinian War – Battle of Varese: Giuseppe Garibaldi's Hunters of the Alps confront and defeat Austrian forces, led by Field Marshal-Lieutenant Carl Baron Urban.
- May 26 & June 2 – Geologist Joseph Prestwich and amateur archaeologist John Evans report (to the Royal Society and Society of Antiquaries of London, respectively) the results of their investigations of gravel-pits in the Somme valley and elsewhere, extending human history back to what will become known as the Paleolithic Era.
- May 30 – Battle of Palestro: The Sardinians defeat the Austrian army.
- May 31 – The Great Clock at the Palace of Westminster, London is started.
- June 4 – Austro-Sardinian War – Battle of Magenta: The French and Sardinians defeat the Austrians.
- June 6 – The British Crown colony of Queensland in Australia is created, by devolving part of the territory of New South Wales (Queensland Day).
- June 8 – The discovery of the Comstock Lode in the western Utah Territory sets off the Rush to Washoe.
- June 15 – The so-called Pig War border dispute between the Americans and the British, over the San Juan Islands, begins by the death of the namesake pig.
- June 17 – The only recorded simoom ever in North America hits Goleta and Santa Barbara, California.
- June 18 – Aletschhorn, the second summit of the Bernese Alps, is first ascended.
- June 24 – Battle of Solferino: The Kingdom of Sardinia and the armies of Napoleon III of France defeat Franz Joseph I of Austria in northern Italy; the battle inspires Henri Dunant to found the Red Cross.
- June 30 – Charles Blondin crosses Niagara Falls on a tightrope, for the first time.
- July 1 – The first intercollegiate baseball game is played, between Amherst and Williams Colleges.
- July 8
- July 11 – The chimes of Big Ben ring for the first time in London.
- July 11 – By the preliminary treaty signed at Villafranca, Italy, Lombardy is ceded to the French (who immediately cede it to Sardinia), while the Austrians keep Venetia, and the French promise to restore the Central Italian rulers expelled in the course of the war. This brings the Austro-Sardinian War effectively to a close.
- July 30 – Grand Combin, one of the highest summits in the Alps, is first ascended.
- August 16 – The Tuscan National Assembly formally deposes the House of Habsburg-Lorraine, ending an ascendancy of 109 years.
- August 27 – Edwin Drake drills the first oil well in the United States, near Titusville, Pennsylvania, starting the Pennsylvania oil rush.
- August 28–September 2– The solar storm of 1859, the largest geomagnetic solar storm on record, causes the Northern lights to be visible as far south as Cuba and knocks out telegraph communication (this is also called the Carrington event).
- September – British merchant Thomas Blake Glover begins business in Nagasaki, Japan.
- September 17 – In San Francisco, Joshua Norton proclaims himself to be His Imperial Majesty Emperor Norton I, Emperor of the United States and Protector of Mexico.
- October 16 – John Brown raids the Harpers Ferry Armory in Harper's Ferry, Virginia, in an unsuccessful bid to spark a general slave rebellion.
- October 18 – Troops under Colonel Robert E. Lee overpower John Brown, at the Federal arsenal.
- October 26 – The steamship Royal Charter is wrecked on the coast of Anglesey, Wales, with 454 dead.
- November 1 – The current Cape Lookout, North Carolina, lighthouse is lighted for the first time (its first-order Fresnel lens can be seen for 19 miles).
- November 10 – The Treaty of Zürich, reaffirming the terms of the Treaty of Villafranca, brings the Austro-Sardinian War to an official close.
- November 15 – The first Zappas Olympics open in Greece.
- November 24
- December 2 – Militant abolitionist leader John Brown is hanged for his October 16 raid on Harpers Ferry, West Virginia.
- December 4 – The Mekteb-i Mülkiye School is founded in the Ottoman Empire.
- December 10
- January 6 – Hugh Rodman, American admiral (d. 1940)
- January 8 – Fanny Bullock Workman, American geographer, writer and mountain climber (d. 1925)
- January 11 – George Curzon, 1st Marquess Curzon of Kedleston, British statesman, Viceroy of India (d. 1925)
- January 27 – Wilhelm II of Germany, last Emperor of Germany and King of Prussia (d. 1941)
- January 29 – Virginie Amélie Avegno Gautreau, Parisian socialite, model for the painting Portrait of Madame X (d. 1915)
- February 1
- February 3 – Hugo Junkers, German industrialist, aircraft designer (d. 1935)
- February 6 – Elias Disney, American farmer, father of Walt Disney (d. 1941)
- February 10 – Alexandre Millerand, President of France (d. 1943)
- February 14
- February 19 – Svante Arrhenius, Swedish chemist, Nobel Prize laureate (d. 1927)
- February 25 – Vasil Kutinchev, Bulgarian general (d. 1941)
- February 26 – Louise DeKoven Bowen, American philanthropist, activist (d. 1953)
- February 28 – Florian Cajori, Swiss historian of mathematics (d. 1930)
- March 2 – Sholem Aleichem, Ukrainian Yiddish novelist (d. 1916)
- March 4 – Alexander Stepanovich Popov, Russian physicist (d. 1905)
- March 8 – Kenneth Grahame, English author (d. 1932)
- March 12 – Abraham H. Cannon, American Mormon apostle (d. 1896)
- March 26 – Alfred Edward Housman, English poet (d. 1936)
- April 3
- April 7 – Jacques Loeb, German–American physiologist, biologist (d. 1924)
- April 8 – Edmund Husserl, Austrian philosopher (d. 1938)
- April 17 – Willis Van Devanter, Associate Justice of the Supreme Court of the United States (d. 1941)
- May 1 – Jacqueline Comerre-Paton, French artist (d. 1955)
- May 15 – Pierre Curie, French physicist, Nobel Prize laureate (d. 1906)
- May 22 – Sir Arthur Conan Doyle, Scottish writer (d. 1930)
- June 9 – Doveton Sturdee, British admiral (d. 1925)
- June 21 – Henry Ossawa Tanner, American artist (d. 1937)
- July 6
- July 11 (June 29 O.S.) – Peter Verigin, Russian-born Canadian Doukhobor leader (d. 1924)
- July 13 – Sidney Webb, 1st Baron Passfield, British co-founder of the London School of Economics (d. 1947)
- July 28 – Mary Anderson, American stage actress (d. 1940)
- August 4 – Knut Hamsun, Norwegian author, Nobel Prize laureate (d. 1952)
- August 18 – Anna Ancher, Danish painter (d. 1935)
- September 3 – Jean Jaurès, French socialist (d. 1914)
- September 7 – Margaret Crosfield, British palaeontologist, geologist (d. 1952)
- September 16 – Yuan Shikai, Chinese dictator (d. 1916)
- September 17
- September 18 – Lincoln Loy McCandless, Hawaiian politician, rancher (d. 1940)
- September 19 – Marshall Pinckney Wilder, American actor, humorist, comedian and monologist (d. 1915)
- September 21 – Francesc Macià, Catalan politician (d. 1933)
- September 24 – Radko Dimitriev, Bulgarian and Russian general (d. 1918)
- September 28 – Alfredo Baquerizo, 19th President of Ecuador (d. 1951)
- October 6 – Frank Seiberling, American inventor, cofounder of Goodyear Tire & Rubber Company (d. 1955)
- October 9 – Alfred Dreyfus, French military officer (d. 1935)
- October 12 – Diana Abgar, Armenian diplomat (d. 1937)
- October 18 – Henri Bergson, French philosopher, recipient of the Nobel Prize in Literature (d. 1941)
- October 20 – John Dewey, American philosopher, psychologist, and educator (d. 1952)
- November 14
- November 15 – Christopher Hornsrud, 11th Prime Minister of Norway (d. 1960)
- November 19 – Mikhail Ippolitov-Ivanov, Russian composer (d. 1935)
- November 22 – Fusajiro Yamauchi, Japanese founder of Nintendo (d. 1940)
- November 24 – Cass Gilbert, American architect (Woolworth Building, United States Supreme Court building) (d. 1934)
- November 27 – William Bliss Baker, American painter (d. 1886)
- December 2 – Georges Seurat, French painter (d. 1891)
- December 5 – John Jellicoe, 1st Earl Jellicoe, British admiral (d. 1935)
- December 15 – L. L. Zamenhof, Russo-Polish creator of Esperanto (d. 1917)
- December 17 – Paul César Helleu, French artist (d. 1927)
- December 29 – Venustiano Carranza, 37th President of Mexico (d. 1920)
- January 21 – Henry Hallam, English historian (b. 1777)
- January 28 – F. J. Robinson, 1st Viscount Goderich, Prime Minister of the United Kingdom (b. 1782)
- February 13 – Eliza Acton, English poet, cookery writer (b. 1799)
- February 27 – Philip Barton Key, U.S. District Attorney (b. 1818)
- April 16 – Alexis de Tocqueville, French historian (b. 1805)
- May 6 – Alexander von Humboldt, German naturalist, geographer (b. 1769)
- May 13 – Bakht Khan, commander-in-chief of Indian rebel forces in the Indian Rebellion of 1857 (b. 1797)
- June 11 – Klemens Wenzel von Metternich, Austrian diplomat (b. 1773)
- June 13 – Angélique Brûlon, French soldier, first female Knight of the French Legion of Honour (b. 1772)
- June 23 – Maria Pavlovna, Dowager Grand Duchess of Saxe-Weimar-Eisenach (b. 1786)
- July 8 – King Oscar I of Sweden and Norway (b. 1799)
- July 17 – Queen Stephanie, consort of Pedro V of Portugal (b. 1837)
- July 30 – Richard Rush, United States Attorney General under James Madison, United States Secretary of the Treasury under President John Quincy Adams (b. 1780)
- August 2 – Horace Mann, American educator, abolitionist (b. 1796)
- August 4 – John Vianney, French saint known as the Curé de Ars (b. 1786)
- August 15 – Nathaniel Claiborne, U.S. politician (b. 1777)
- August 28 – Leigh Hunt, British critic, essayist (b. 1784)
- August 28 – Sultan Abd al-Rahman of Morocco (b. 1788)
- September 15 – Isambard Kingdom Brunel, British engineer (b. 1806)
- September 19 – George Bush (biblical scholar), American professor of Asian languages (b. 1796)
- September 28 – Carl Ritter, German geographer (b. 1779)
- October 4 – Karl Baedeker, German author, publisher (b. 1801)
- October 12 – Robert Stephenson, English civil engineer (b. 1803)
- October 22 – Louis Spohr, German violinist, composer (b. 1784)
- November 28 – Washington Irving, American author (b. 1783)
- December 2 – John Brown, American abolitionist (hanged) (b. 1800)
- December 8 – Thomas de Quincey, English writer (b. 1785)
- December 16 – Wilhelm Grimm, German philologist, folklorist (b. 1786)