|Centuries:||18th century – 19th century – 20th century|
|Decades:||1810s 1820s 1830s – 1840s – 1850s 1860s 1870s|
|Years:||1838 1839 1840 – 1841 – 1842 1843 1844|
- January 26 – The United Kingdom occupies Hong Kong. Later during the year, the first census of the island recorded a population of about 7,500.
- February 18 – The first ongoing filibuster in the United States Senate begins and lasts until March 11.
- March 4 – Martin Van Buren, President of the United States is succeeded by William Henry Harrison.
- March 9 – The Supreme Court of the United States rules in the Amistad case that the Africans who seized control of the ship had been taken into slavery illegally.
- April 4 – US President William Henry Harrison dies of pneumonia becoming the first President of the United States to die in office and at one month, the elected president with the shortest term served. He is succeeded by Vice President John Tyler.
- August 16 – U.S. President John Tyler vetoes a bill which called for the re-establishment of the Second Bank of the United States. Enraged Whig Party members riot outside the White House in the most violent demonstration on White House grounds in U.S. history.
- September 24 – United Kingdom annexes Sarawak from Brunei; James Brooke is appointed rajah
- November 13 – James Braid first sees a demonstration of animal magnetism, which leads to his study of the subject he eventually calls hypnosis.
- The two colonies of the Canadas are merged into the Province of Canada.
- Queen's University is founded in Kingston, Canada, by Rev. Thomas Liddell, who carried a Royal Charter from Queen Victoria and became the school's first Principal.
- Fordham University is founded in The Bronx by the Society of Jesus. Its name at founding is St. John's College.
- With the help of industrial espionage, August Borsig builds the first German locomotives.
- January 7 – Bernadette Soubirous, a visionary from Lourdes. (died 1879)
- January 14 – Berthe Morisot, French painter (died 1895)
- January 25 – Jackie Fisher, British admiral (died 1920)
- January 28 – Henry Morton Stanley, Welsh explorer and journalist (died 1904)
- February 2 – François-Alphonse Forel, Swiss hydrologist (died 1912)
- February 4 – Clément Ader, French engineer, inventor, and airplane pioneer (died 1926)
- February 25 – Pierre-Auguste Renoir, French painter (died 1919)
- March 8 – Oliver Wendell Holmes, Jr., U.S. Supreme Court Justice (died 1935)
- April 13 – Louis-Ernest Barrias, French sculptor (died 1905)
- May 10 – James Gordon Bennett, Jr., American newspaper publisher (died 1918)
- July 29 – Gerhard Armauer Hansen, Norwegian doctor and scientist (d. 1912)
- August 25 – Emil Kocher, Swiss medical researcher, recipient of the Nobel Prize in Physiology or Medicine (died 1917)
- September 8 – Antonín Dvořák, Czech composer (died 1904)
- September 28 – Georges Clemenceau, French statesman (died 1929)
- October 7 – King Nicholas I of Montenegro (died 1921)
- October 16 – Prince Hirobumi Ito, Japanese governor of Korea (died 1909)
- November 6 – Nelson W. Aldrich, Senator from Rhode Island (died 1915)
- November 9 – King Edward VII of the United Kingdom (died 1910)
- November 20 – Wilfrid Laurier, seventh Prime Minister of Canada (died 1919)
- December 6 – Frédéric Bazille, French painter (died 1870)
- December 20 – Ferdinand Buisson, French pacifist, recipient of the Nobel Peace Prize (died 1932)
- February 17 – Ferdinando Carulli, Italian guitarist
- March 1 – Claude Victor-Perrin, duc de Belluno, French marshal (born 1764)
- April 4 – William Henry Harrison, 9th President of the United States (born 1773)
- April 28 – Peter Chanel, French Roman Catholic missionary (martyred) (born 1803)
- May 20 – Joseph Blanco White, British theologian (born 1775)
- May 23 – Franz Xaver von Baader, German philosopher and theologian (born 1765)
- June 1 – David Wilkie, Scottish artist (born 1785)
- June 1 – Nicolas Appert, French inventor (born 1749).
- August 24 – Theodore Edward Hook, English writer (born 1788)