1816 (MDCCCXVI) was a leap year starting on Monday (dominical letter GF) of the Gregorian calendar and a leap year starting on Saturday (dominical letter BA) of the Julian calendar, the 1816th year of the Common Era (CE) and Anno Domini (AD) designations, the 816th year of the 2nd millennium, the sixteenth year of the 19th century, and the seventh year of the 1810s decade. Note that the Julian day for 1816 is 12 calendar days difference, which continued to be used from 1582 until the complete conversion of the Gregorian calendar was entirely done in 1929.
This year was known as the 'Year Without a Summer' because of low temperatures in the Northern Hemisphere, the result of the Mount Tambora volcanic eruption in Indonesia in 1815. The sulfur from this eruption reflected the sun's rays and caused global cooling.
- January 6 – Tsar Alexander I of Russia signs an order for the expulsion of the Jesuits from St. Petersburg and Moscow.
- January 9 – Sir Humphry Davy's Davy lamp is first tested underground as a coal mining safety lamp at Hebburn Colliery in north east England.
- January 17 – Fire nearly destroys the city of St. John's, Newfoundland.
- February 8 – The Governorate of Estonia of the Russian Empire emancipates its peasants from serfdom.
- February 10 – Friedrich Karl Ludwig, Duke of Schleswig-Holstein-Sonderburg-Beck, dies and is succeeded by Friedrich Wilhelm, his son and founder of the House of Glücksburg.
- February 20 – Gioachino Rossini's opera buffa The Barber of Seville premières at the Teatro Argentina in Rome.
- April 10 – The Second Bank of the United States obtains its charter.
- April 11 – In Philadelphia, the African Methodist Episcopal Church is established by Richard Allen and additional African-American Methodists, the first such denomination completely independent of White churches.
- May 2 – Leopold of Saxe-Coburg (later King of the Belgians) marries Charlotte Augusta, but she dies the next year.
- June 19 – Battle of Seven Oaks: The Hudson's Bay Company is defeated by the North West Company, near Winnipeg, Canada.
- July – Lord Byron, Mary Wollstonecraft Godwin, Percy Bysshe Shelley and John Polidori, gathered at the Villa Diodati by Lake Geneva in a rainy Switzerland, tell each additional tales. This gives rise to two classic Gothic narratives, Mary Shelley's Frankenstein and Polidori's The Vampyre.
- July 9 – The United Provinces of South America declares independence from Spain.
- July 17 – The French passenger ship Medusa runs aground off the coast of Senegal, with 140 lives lost in the botched rescue that takes weeks, leading to a scandal in the French government.
- August 14 – The United Kingdom formally annexes the Tristan da Cunha archipelago in the southern Atlantic Ocean, ruling it from the Cape Colony.
- August 24 – The Treaty of St. Louis is signed in St. Louis.
- August 27 – Bombardment of Algiers: Various European Allies ships force Omar Agha, Dey of Algiers to free Christian slaves.
- October 21 – Penang Free School is founded by Rev. Sparke Hutchings on the island of Penang (in modern-day Malaysia).
- November 6 – James Monroe defeats Rufus King in the United States presidential election.
- November 19 – University of Warsaw established.
- December 11 – Indiana is admitted as the nineteenth U.S. state.
- December 12 – Merger of the thrones of Sicily and Naples into the Kingdom of the Two Sicilies under King Ferdinand I.
- December 21 – American Colonization Society established to support the emigration of free African Americans to Africa.
- Shaka starts to rule the Zulu Kingdom at about this date.
- Banjul, capital of the Gambia, is founded as a trading post named Bathurst.
- René Laennec invents the stethoscope.
- E. Remington and Sons (the famous firearm and later typewriter manufacturing company) is founded in the United States.
- Robert Stirling patents his Stirling engine, at this time known as Stirling's air engine.
- A rail capable of supporting a heavy locomotive is developed.
- January 3 – Samuel C. Pomeroy, American politician and railroad executive (d. 1891)
- January 30 – Nathaniel P. Banks, American politician and general (d. 1894)
- March 14 – William Marsh Rice, American university founder (d. 1900)
- March 29 – Tsultrim Gyatso, tenth Dalai Lama of Tibet (d. 1837)
- April 21 – Charlotte Brontë, English novelist and poet (d. 1855)
- April 22 – Charles-Denis Bourbaki, French general (d. 1897)
- April 25 – Eliza Daniel Stewart, American temperance movement leader (d. 1908)
- May 24 – Emanuel Leutze, German American painter (d. 1868)
- June 19 – William Henry Webb, American industrialist and philanthropist (d. 1899)
- June 30 – Richard Lindon, English inventor of the rugby ball (d. 1887)
- July 4 – Arthur de Gobineau, French diplomat and author (d. 1882)
- July 21 – Paul Reuter, German entrepreneur (d. 1899)
- July 23 – Charlotte Cushman, American actress (d. 1876)
- July 31 – George Henry Thomas, American general (d. 1870)
- August 4 – William Julian Albert, U.S. Congressman (d. 1879)
- August 14 – Félix Douay, French General (d. 1879)
- August 16 – Charles John Vaughan, English scholar (d. 1897)
- September 11 – Carl Zeiss, German maker of optical instruments (d. 1888)
- October 22 – Prince Yamashina Akira (d. 1891)
- November 3 – Jubal Early, American Confederate general (d. 1894)
- November 17 – August Wilhelm Ambros, Austrian composer (d. 1876)
- December 13 – Werner von Siemens, German inventor and industrialist (d. 1892)
- December 14 – Abraham Hochmuth, Hungarian rabbi (d. 1889)
- December 29 – Carl Ludwig, German physician and physiologist (d. 1895)
- date unknown – Wazir Akbar Khan, Afghan prince and general (d. 1845)
- January 5 – George Prévost, British general and colonial administrator (b. 1767)
- January 27 – Samuel Hood, first Viscount Hood, British admiral (b. 1724)
- February 6 – Maria Ludwika Rzewuska, Polish szlachcianka (b. 1744)
- February 22 – Adam Ferguson, Scottish philosopher and historian (b. 1723)
- March 3 – Johann August von Starck, German pastor (b. 1741)
- March 19 – Philip Mazzei, Italian physician and friend of Thomas Jefferson (b. 1730)
- March 20 – Queen Maria I of Portugal (b. 1734)
- March 31 – Francis Asbury, American Methodist bishop (b. 1745)
- May 4 – Samuel Dexter, American solicitor and politician, fourth United States Secretary of War, third United States Secretary of the Treasury (b. 1761)
- June 5 – Giovanni Paisiello, Italian composer (b. 1751)
- June 12 – Pierre Augereau, Marshal of France and duc de Castiglione (b. 1757)
- July 5 – Dorothea Jordan, Irish-born actress, mistress of King William IV of the United Kingdom (b. 1761)
- July 7 – Richard Brinsley Sheridan, Irish-born playwright (b. 1751)
- July 14 – Francisco de Miranda, Venezuelan revolutionary (b. 1750)
- August 9 – Johann August Apel, German writer and jurist (b. 1771)
- September 22 – Sir Robert Gunning, first Baronet, British diplomat (b. 1731)
- September 27 – Edward Charles Howard, English chemist and chemical engineer (b. 1774)
- November 6 – Charles II, Grand Duke of Mecklenburg-Strelitz (b. 1741)
- November 8 – Gouverneur Morris, American statesman (b. 1752)
- December 15 – Charles Stanhope, third Earl Stanhope, English statesman and scientist (b. 1753)
- December 30 – Louis Henri Loison, French general (b. 1771)