- April 9 – The world's first commercial electric telegraph line comes into operation, alongside the Great Western Railway line in England, from London Paddington station to West Drayton.
- April 19 – The Treaty of London establishes Belgium as a kingdom, with its independence and neutrality guaranteed by the great powers of Europe. Half of the Limburg province of Belgium is added to the Netherlands, giving rise to a Belgian Limburg and Dutch Limburg (the latter being joined (from September 5) to the German Confederation).
- May 7 – The Bedchamber Crisis begins in the United Kingdom, after Prime Minister Lord Melbourne announces his resignation.  Queen Victoria asks several MPs to form a new government, and they insist on the condition that the Queen dismiss several of her personal attendants, the ladies of the bedchamber, for political reasons.
- May 12 – Socialist activist Louis Auguste Blanqui and the Société des Saisons begin an uprising against the government of France. The insurrection is suppressed, but not before 50 people are killed and 190 wounded. Blanqui is imprisoned until 1848. 
- May 22 – Former British statesman Lord Durham, as President of the New Zealand Company, formally asks the British government for permission to colonize New Zealand, and to establish a colonial government under the sovereignty of the United Kingdom. 
- May 23 – Turkish troops cross the Euphrates River and invade Syria, but are defeated in battle in June. 
- June 3 – Destruction of opium at Humen begins, casus belli for Britain to open the 3-year First Opium War against Qing Dynasty China. A rapid rise in the sale of opium in China to over 40,000 chests (~56,000 kilograms (123,000 lb)) per annum results.  has caused the Chinese government to dispatch scholar-official Lin Zexu to Guangzhou to deal with the growing problem of opium addiction.
- June 22 – Louis Daguerre receives a patent for his camera (commercially available by September at the price of 400 francs).
- October 3 – In the Kingdom of the Two Sicilies, a railway between Naples and Portici (7.4 km length) is inaugurated by King Ferdinand II of Bourbon, as the first railway in the Italian Peninsula.
- October 15 – Abdelkader El Djezairi declares a jihad against the French.
- November 4 – The Newport Rising is the last large-scale armed rebellion against authority, in mainland Britain.
- November 11 – The Virginia Military Institute is founded in Lexington, Virginia.
- November 17 – Giuseppe Verdi's first opera, Oberto, conte di San Bonifacio, opens in Milan.
- November 25 – A disastrous cyclone slams India with terrible winds and a giant 40-foot storm surge, wiping out the port city of Coringa; 300,000 people die.
- November 27 – In Boston, Massachusetts, the American Statistical Association is founded.
- December 6 – In Harrisburg, Pennsylvania, at its first ever national convention, the Whig Party nominates former U.S. Army General William Henry Harrison, to be its candidate for President of the United States in the 1840 election. Although Senator Henry Clay of Kentucky had received 103 of the 128 necessary votes on the first ballot, he receives only 90 on the final vote, while Harrison gets 148. Former U.S. Senator John Tyler is unanimously nominated for Vice President. 
- January 2 – Gustave Trouvé, French electrical engineer, inventor (d. 1902)
- January 8 – William Andrews Clark, American politician, entrepreneur (d. 1925)
- January 9 – John Knowles Paine, first well-known American-born composer of large-scale orchestral music (d. 1906)
- January 19 – Paul Cézanne, French painter (d. 1906)
- January 26 – Rachel Lloyd, American chemist (d. 1900)
- February 6 – Caroline Testman, Danish women's rights activist (d. 1919)
- February 11
- February 18 – Pascual Cervera y Topete, Spanish admiral (d. 1909)
- February 22 – Francis Pharcellus Church, American editor, publisher (d. 1906)
- March 3 – Jamsetji Tata, Indian Parsi businessman (d. 1904)
- March 8
- March 9 – Phoebe Knapp, American hymn writer (d. 1908)
- March 15 – Daniel Ridgway Knight, American artist (d. 1924)
- March 16
- March 21 – Modest Mussorgsky, Russian composer (d. 1881)
- March 23 – Julius von Hann, Austrian meteorologist (The father of modern meteorology) (d. 1921)
- March 25 – Marianne Hainisch, founder, leader of the Austrian women's movement (d. 1936)
- March 27 – John Ballance, 14th Premier of New Zealand (d. 1893)
- April 3 – Karl, Freiherr von Prel, German philosopher (d. 1899)
- April 12 – Nikolay Przhevalsky, Russian explorer (d. 1888)
- April 16 – Antonio Starabba, Marchese di Rudinì, Prime Minister of Italy (d. 1908)
- April 30 – Floriano Peixoto, Brazilian president (d.1895)
- May 21 – Nils Christoffer Dunér, Swedish astronomer (d. 1914)
- June 1 – Abdyl Frashëri, Albanian politician [d.1892)
- June 10 – Ludvig Holstein-Ledreborg, Prime Minister of Denmark (d. 1912)
- June 17 – Arthur Tooth, Anglican clergyman prosecuted for Ritualist practices in the 1870s (d. 1931)
- June 21 – Machado de Assis, Brazilian author (d. 1908)
- July 8 – John D. Rockefeller, American industrialist, philanthropist (d. 1937)
- July 17 – Ephraim Shay, American inventor of the Shay locomotive (d. 1916)
- July 28 – Isabelle Gatti de Gamond, Italo-Belgian educationalist, feminist and politician (d. 1905)
- July 31 – Ignacio Andrade, 37th President of Venezuela (d. 1925)
- August 4 – Walter Pater, English essayist, critic (d. 1894)
- August 8 – Nelson A. Miles, American general (d. 1925)
- August 15 – Antonín Petrof, Czech piano maker (d. 1915)
- September 2 – Henry George, American writer, politician and political economist (d. 1897)
- September 7 – Patricio Montojo, Spanish admiral (d. 1917)
- September 10 – Charles Sanders Peirce, American philosopher, logician, mathematician and scientist (d. 1914)
- October 2 – Oscar de Négrier, French general (d. 1913)
- October 9
- October 30 – Alfred Sisley, French Impressionist landscape painter (d. 1899)
- November 1 – Pál Luthár, Slovene writer in Hungary (d. 1919)
- November 12 – Frank Furness, American architect, soldier (d. 1912)
- November 18
- November 20 – Christian Wilberg, German painter (d. 1882)
- December 5 – George Armstrong Custer, American cavalry officer (d. 1876)
- December 7 – Redvers Buller, British general, Victoria Cross recipient (d. 1908)
- December 12 – Caroline Ingalls (b. Caroline Lake Quiner), American pioneer, mother of author Laura Ingalls Wilder (d. 1924)
- December 23 – János Murkovics, Slovene writer, teacher in Hungary (d. 1917)
- January 24 – Michele Cachia, Maltese architect, military engineer (b. 1760)
- February 7 – Karl August Nicander, Swedish poet (b. 1799)
- February 10 – Pedro Romero, Spanish torero (b. 1754)
- March 2 – Charlotte Napoléone Bonaparte, niece of Napoleon I of France (b. 1802)
- April 1 – Benjamin Pierce, American politician (b. 1757)
- April 2 – Hezekiah Niles, American editor, publisher (b. 1777)
- April 4 – Queen Kaahumanu II of Hawaii
- April 11 – John Galt, Scottish novelist (b. 1779)
- April 22 – Denis Davydov, Russian general, poet (b. 1784)
- May 11 – Thomas Cooper, American political philosopher (b. 1759)
- May 17 – Archibald Alison, Scottish author (b. 1757)
- June 23 – Lady Hester Stanhope, English archaeologist (b. 1776)
- June 27 – Ranjit Singh, Maharaja of The Punjab (Sikh Empire) (b. 1780)
- July 1 – Mahmud II, Ottoman sultan (b. 1785)
- July 8 – Fernando Sor, Spanish guitarist, composer (b. 1778)
- July 15 – Winthrop Mackworth Praed, English politician, poet (b. 1802)
- July 16 – Chief Bowles, Cherokee leader (b. ~1756)
- August 10 – Sir John St Aubyn, 5th Baronet, English fossil collector (b. 1758)
- August 22 – Benjamin Lundy, American abolitionist (b. 1789)
- August 28 – William Smith, English geologist, cartographer (b. 1769)
- September 29 – Friedrich Mohs, German geologist, mineralogist (b. 1773)
- October 6 – William Light, British Army colonel, first Surveyor-General of South Australia (b. 1786)
- October 11 – Leonor de Almeida Portugal, 4th Marquise of Alorna, Portuguese painter, poet (b. 1750)
- November 15 – William Murdoch, Scottish inventor (b. 1754)
- December 3 – Frederick VI, King of Denmark, ex-King of Norway (b. 1768)
- December 15 – Ignaz Aurelius Fessler, Hungarian court councillor, minister to Alexander I (b. 1756)
- ^ Mark Hovell, The Chartist Movement (Manchester University Press, 1966) p143
- ^ Jill Harsin, Barricades: The War of the Streets in Revolutionary Paris, 1830-1848 (Palgrave Macmillan, 2002) p124
- ^ T. Lindsay Buick, The French at Akaroa: An Adventure in Colonization (Cambridge University Press, 1928)(reprinted 2011) p294
- ^ Charles Alan Fyffe, A History of Modern Europe, Volume 2 (Cassell & Company, 1886) p453
- ^ Greenberg, Michael. British Trade and the Opening of China 1800-1841 (preview). p. 113.
expansion in imports from 16,550 chests in the season 1831-2 to over 30,000 in 1835-6, and 40,000 in 1838-9
- ^ Ebrey, Patricia Buckley, ed. (2010). "Chapter 9: Manchus and Imperialism: The Qing Dynasty 1644–1900". The Cambridge Illustrated History of China (2nd ed.). Cambridge University Press. p. 236. ISBN 978-0-521-19620-8.
- ^ Stan M. Haynes, The First American Political Conventions: Transforming Presidential Nominations, 1832-1872 (McFarland, 2012) p54
- ^ Gardner, Alexander. "XII". Memoirs Of Alexander Gardner - Colonel of Artillery in the Service of Maharaja Ranjit Singh. William Blackwood & Sons. p. 211.