January 15 – The French newspaper Le Figaro begins publication in Paris, initially as a weekly.
January 30 – The Menai Suspension Bridge, built by engineer Thomas Telford, is opened between the island of Anglesey and the mainland of Wales.
February 8 – Unitarian Bernardino Rivadavia becomes the first President of Argentina.
February 11
University College London is founded, under the name University of London.
Swaminarayan writes the Shikshapatri, an important text within Swaminarayan Hinduism.
February 13 – The American Temperance Society is founded.
February 23 – Russian Mathematician Nikolai Ivanovich Lobachevsky develops non-Euclidean geometry (independently of Janos Bolyai).
February 24 – The Treaty of Yandabo ends the First Anglo-Burmese War; Britain gains Assam, Manipur, Rakhine and Tanintharyi.
March 1 – Chunee, a male Asian elephant is put down after running amok the week before, killing one of his keepers. After arsenic and shooting fail, he was killed with a sword.
March 10 – João VI, King of Portugal and the former Emperor of Brazil, dies after a short illness that had started six days earlier, after he had been served dinner while visiting Jerónimos Monastery. An investigative autopsy 174 years later will discover that he had been killed by arsenic poisoning. King João's son, Emperor Pedro I of Brazil, sails back to Portugal and briefly reigns as King Pedro IV, before turning over the Portuguese throne to his daughter, Maria.
April 1 – Samuel Morey patents an internal combustion engine in the United States.
April 10 – The Third Siege of Missolonghi ends, with the massacre of thousands of Greek defenders by the Ottoman besiegers.
May 28 – Pedro I of Brazil abdicates as King of Portugal.
June – Photography: Nicéphore Niépce makes a true photograph.
June 14–15 – The Auspicious Incident: Mahmud II, sultan of Ottoman Empire, crushes the last mutiny of janissaries in Istanbul.
June 21 – Greek War of Independence: The attempted Ottoman–Egyptian invasion of Mani begins.