|Wikimedia Commons has media related to 1843.|
1843 (MDCCCXLIII)was a common year starting on Sunday of the Gregorian calendar and a common year starting on Friday of the Julian calendar, the 1843rd year of the Common Era (CE) and Anno Domini (AD) designations, the 843rd year of the 2nd millennium, the 43rd year of the 19th century, and the 4th year of the 1840s decade. As of the start of 1843, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.
- The House of Jamalullail is established at Perlis Darul Sunnah (now known as Perlis Darul Sunnah, Malaysia).
- Shaikh Ali bin Khalifa Al-Khalifa captures the fort and town of Riffa after the rival
branch of the family fails to gain control of the Riffa Fort and flees to Manama. Shaikh Mohamed bin Ahmed is killed at the battle, called the Battle of Hunayniya.
- January 3 – The Illustrated Treatise on the Maritime Kingdoms (海國圖志, Hǎiguó Túzhì) compiled by Wei Yuan and others, the first significant Chinese work on the West, is published in China.
- January 6 – Antarctic explorer James Clark Ross discovers Snow Hill Island.
- January 20 – Honório Hermeto Carneiro Leão, Marquis of Paraná, becomes de facto first prime minister of the Empire of Brazil.
- February 3 – Uruguayan Civil War: Argentina supports Oribe of Uruguay, and begins a siege of Montevideo.
- February 6 – The Virginia Minstrels perform the first minstrel show, at the Bowery Amphitheatre in New York City.
- February 8 – An earthquake hits the Caribbean island of Guadeloupe, killing 1,500-5000 people.
- February 11 – Giuseppe Verdi's opera I Lombardi alla prima crociata premieres at La Scala in Milan.
- February 14 – The event that inspired the Beatles song Being for the Benefit of Mr. Kite! is held in England.
- February 25 – Paulet Affair: Lord George Paulet occupies the Kingdom of Hawaii, in the name of Great Britain.
- March 8 – The Danish government re-establishes the Althing in Iceland as an advisory body, by royal decree.
- March 11–14– Eta Carinae flares, to become the second-brightest star.
- March 13 – Catawba County, North Carolina is created, and its first court is held in Mathias Barringer Jr.'s house.
- March 15 – Victoria, British Columbia, is founded by the Hudson's Bay Company as a trading post and fort.
- March 16 – The city of Petrópolis is founded by the government of Brazil.
- March 21 – The world does not end, contrary to the first prediction by American preacher William Miller.
- March 24 – Battle of Hyderabad: The Bombay Army, led by Major General Sir Charles Napier, defeats the Talpur Emirs, securing Sindh as a province of British India.
- March 25 – Marc Isambard Brunel's Thames Tunnel, the first tunnel under the River Thames and the world's first bored underwater tunnel, is opened in London.
- July 1 – Ulysses S. Grant (21st) and John J. Peck (8th) graduate from a class of 39 at the United States Military Academy, West Point.
- July 12 – Origin of Latter Day Saint polygamy: Joseph Smith, founder of the Latter Day Saint movement in the United States, receives a revelation recommending polygamy.
- July 19 – Isambard Kingdom Brunel's SS Great Britain is launched from Bristol; it will be the first iron-hulled, propeller-driven ship to cross the Atlantic Ocean.
- July 25 – Père Antoine Désiré Mégret, a Capuchin missionary, purchases for $900 the land that will become Abbeville, Louisiana, a town founded by descendants of Acadians from Nova Scotia.
- August 1 – Brazil becomes the second country, after Great Britain, to issue nationally valid postage stamps, with the release of its Bull's Eye series.
- August 15 – Tivoli Gardens, one of the oldest still intact amusement parks in the world, opens in Copenhagen, Denmark.
беларуская (тарашкевіца): 1843
srpskohrvatski / српскохрватски: 1843