- January 1 – The importation of slaves into the United States is banned, as the 1806 Act Prohibiting Importation of Slaves takes effect; African slaves continue to be imported into Cuba, and until Cuba abolishes slavery in 1865, half a million slaves will arrive on the island.
- January 12 – The organizational meeting leading to the creation of the Wernerian Natural History Society, a former Scottish learned society, is held in Edinburgh.
- January 12 – John Rennie's scheme to defend St Mary's Church, Reculver, founded in 669, from coastal erosion is abandoned in favour of demolition, despite the church being an exemplar of Anglo-Saxon architecture and sculpture.
- January 22 – The Bragança Portuguese Royal Family arrives in Brazil, fleeing from the French army.
- January 26 – Rum Rebellion: On the 20th anniversary of the foundation of the colony of New South Wales, disgruntled military officers of the New South Wales Corps (the Rum Corps) overthrow and imprison Governor William Bligh, and seize control of the colony.
- February 2 – French troops occupy the Papal States.
- February 6 – The ship Topaz (from Boston April 5, 1807, hunting seals) rediscovers the Pitcairn Islands; only one HMS Bounty mutineer is still alive, (John Adams), who is using the pseudonym Alexander Smith.
- February 11 – In Wilkes-Barre, Pennsylvania, Jesse Fell becomes the first person in the world to burn anthracite coal, as residential heating fuel.
- February 21 –
- March 1 – The slave trade is abolished by the United Kingdom in all of its colonies, as the act of January 22, 1807 takes effect.
- March 2
- March 8 – Brazil: With the arrival of the Portuguese royal family in Brazil, the colony becomes the seat of Portuguese Empire.
- March 11 – Russian troops occupy Tampere.
- March 13 – Upon the death of Christian VII, Frederick VI becomes king of Denmark. The next day (March 14), Denmark declares war on Sweden.
- March 19 – Charles IV of Spain abdicates in favor of his son, Ferdinand VII.
- March 22
- A volcano erupts from an unknown location in the western Pacific. This causes a localized drop in marine air temperatures during this year, and a worldwide drop in marine air temperature for the following decade.
- Prussian philosopher Johann Gottlieb Fichte publishes his Addresses to the German Nation, having delivered them over the winter at the Prussian Academy of Sciences in Berlin, before crowded audiences.
- April 6 – John Jacob Astor incorporates the American Fur Company.
- April 16 – Troops under Colonel Carl von Döbeln clash with Russian troops, in Pyhäjoki, Finland.
- May 2 – Peninsular War – Dos de Mayo Uprising: The people of Madrid rise up against the French troops.
- May 3
- June 12 – Finnish War: A landing of Swedish troops at Ala-Lemu, near Turku, fails.
- June 19 – Finnish War: A second landing of Swedish troops at Ala-Lemu fails.
- June 30
- Finnish War – Battle of Turku: The Swedish archipelago fleet defeats the Russians.
- Humphry Davy informs the Royal Society of London of his isolation and discovery of two elements by electrolysis. From lime, he has produced calcium and established that lime is calcium oxide; by heating boric acid and potassium in a copper tube, he creates a substance he calls boracium, and which is eventually called boron.
- October 6 – English chemist Humphry Davy electrochemically isolates potassium from potash.
- November 8 – 1808 United States presidential election: James Madison defeats Charles C. Pinckney, winning 122 electoral votes to Pinckney's 47. Ten of the 17 states choose their electors by popular vote, the rest choose through state legislatures. George Clinton, who is separately elected as Vice President, gets six electoral votes for President.
- November 12 – Four large French frigates under the command of Jacques Félix Emmanuel Hamelin, including the Venus, are sent to operate from Isle de France (Mauritius) against British trade in the Indian Ocean, triggering the Mauritius campaign of 1809–11.
- November 15 – Mahmud II (1808–1839) succeeds Mustafa IV (1807–1808), as sultan of the Ottoman Empire.
- November 19 – A new truce at Olkijoki ends fighting in Finland, and Swedish troops concede that area to Russia.
- November 23 – Battle of Tudela: French Marshal Lannes defeats a Spanish army.
- December 1 – Tsar Alexander I of Russia proclaims Finland a part of Russia.
- December 4 – Napoleon joins his army in Spain.
- December 9 – At 20:34 UTC, Mercury occults Saturn (there are no observation records).
- December 20 – The original Covent Garden Theatre in London is destroyed by a fire, along with most of the scenery, costumes and scripts.
- December 20 – Peninsular War: The Siege of Zaragoza begins.
- December 22 – Beethoven concert of 22 December 1808: Ludwig van Beethoven conducts and plays piano in a marathon benefit concert, at the Theater an der Wien in Vienna, consisting entirely of first public performances of works by him, including Symphony No. 5, Symphony No. 6, Piano Concerto No. 4 and Choral Fantasy.
- January 6 – Joseph Pitty Couthouy, American naval officer (d. 1864)
- January 13 – Salmon P. Chase, American politician, Chief Justice of the United States (d. 1873)
- January 19 – Lysander Spooner, American philosopher (d. 1887)
- January 27 – David Strauss, German theologian (d. 1874)
- February 5 – Carl Spitzweg, German painter (d. 1885)
- February 26 – Honoré Daumier, French painter, illustrator, and sculptor (d. 1879)
- March 1 – Edward "Ned" Kendall, American bandleader, instrumentalist (keyed bugle) (d. 1861)
- March 17 – Pierre-Louis Dietsch, French composer, conductor (d. 1865)
- March 19 – José María Urvina, 5th President of Ecuador (d. 1891)
- April 13 – Antonio Meucci, Italian-born inventor (d. 1889)
- April 20 – Napoleon III, Emperor of the French (d. 1873)
- May 6 – William Strong, American politician, Associate Justice of the Supreme Court of the United States (d. 1895)
- May 9 – John Scott Russell, Scottish civil engineer (d. 1882)
- May 18 – Venancio Flores, general, president of Uruguay (d. 1868)
- May 21 – David de Jahacob Lopez Cardozo, Dutch Talmudist (d. 1890)
- May 22 – Gérard de Nerval, French writer (d. 1855)
- May 30 – Caroline Chisholm, Australian humanitarian (d. 1877)
- June 3 – Jefferson Davis, President of the Confederate States (d. 1889)
- June 13 – Patrice de MacMahon, Duke of Magenta, French general and politician, first president of the Third Republic (1875-1879) (d. 1893)
- June 16 – James Frederick Ferrier, Scottish metaphysical writer and philosopher (d. 1864)
- June 17 – Henrik Wergeland, Norwegian author (d. 1845)
- June 20 – Samson Raphael Hirsch, German rabbi (d. 1888)
- July 9 – Alexander William Doniphan, American lawyer, military leader (d. 1887)
- July 16 – Daniel Wells Jr., American politician (d. 1902)
- September 7 – William Lindley, English sanitary engineer (d. 1900)
- September 9 – Wendela Hebbe, Swedish journalist (d. 1899)
- September 15 – John Hutton Balfour, Scottish botanist (d. 1884)
- September 29 – Henry Bennett, American politician (d. 1868)
- October 6 – King Frederick VII of Denmark (d. 1863)
- October 20 – Karl Andree, German geographer (d. 1875)
- November 1 – John Taylor, American Mormon leader (d. 1887)
- November 2 – Jules Amédée Barbey d'Aurevilly, French writer (d. 1889)
- November 6 – Friedrich Julius Richelot, German mathematician (d. 1875)
- November 29 – William F. Johnston, American politician (d. 1872)
- December 29 – Andrew Johnson, 17th President of the United States (d. 1875)
- January 4 – Prince Benedetto, Duke of Chablais, Italian general in the French Revolution (b. 1741)
- January 5 – Alexei Grigoryevich Orlov, Russian soldier and statesman (b. 1737)
- January 8 – William Linn, American President of Queen's College) (b. 1752)
- February 12 – Anna Maria Bennett, English novelist (d. 1750)
- February 14 – John Dickinson, American lawyer, governor of Delaware and Pennsylvania (b. 1732)
- March 13 – King Christian VII of Denmark (b. 1749)
- May 18 – Elijah Craig, American minister, inventor (b. 1738)
- March 19 – John Redman (physician), American physician (b. 1722)
- May 28 – Richard Hurd, English bishop, writer (b. 1720)
- September 3 – John Montgomery, American delegate to the Continental Congress (b. 1722)
- September 5 – John Home, Scottish writer (b. 1722)
- September 6 – Louis-Pierre Anquetil, French historian (b. 1723)
- September 13 – Saverio Bettinelli, Italian writer (b. 1718)
- September 17 – Benjamin Bourne, American politician (b. 1755)
- October 1 – Carl Gotthard Langhans, German architect (b. 1732)
- October 9 – John Claiborne, U.S. politician (b. 1777)
- November 3 – Theophilus Lindsey, English theologian (b. 1723)
- November 10 – Guy Carleton, 1st Baron Dorchester, British soldier, governor of Quebec (b. 1724)
- November 17 – David Zeisberger, Moravian missionary (b. 1721)
- ^ Joseph R. Conlin, The American Past: A Survey of American History (Cengage Learning, 2008)
- ^ E. I. Kouri and Jens E. Olesen, eds. The Cambridge History of Scandinavia: Volume 2, 1520–1870 (Cambridge University Press, 2016)
- ^ Antigua and the Antiguans: A Full Account of the Colony and Its Inhabitants (1844, reprinted by Cambridge University Press, 2011) p136
- ^ Chenoweth, M. (2001), Two major volcanic cooling episodes derived from global marine air temperature, AD 1807–1827, Geophys. Res. Lett., 28(15), 2963–2966, doi:10.1029/2000GL012648.
- ^ Marco Fontani, Mariagrazia Costa and Mary Virginia Orna, The Lost Elements: The Periodic Table's Shadow Side (Oxford University Press, 2014)
- ^ "England's Greatest Chemist, Sir Humphry Davy", by John A. Bowes, in Young England magazine (Sunday School Union, 1883) p63
- ^ Thomas Hudson McKee, The National Conventions and Platforms of All Political Parties (Friedenwald, 1901) p18
- ^ William James and Frederick Chamier, The Naval History of Great Britain, Volume 5 (Macmillan and Company, 1902) p53
- ^ Jón Stefánsson, Denmark and Sweden: With Iceland and Finland (T.F. Unwin, Ltd., 1916) p332
- ^ Edward C. Thaden, Russia's Western Borderlands, 1710-1870 (Princeton University Press, 2014) p85
- ^ James Harvey Robinson and Charles A. Beard, eds., Outlines of European History: From the opening of the eighteenth century to the present day (Ginn and Company, 1912) p214