Japan adopts the Gregorian calendar.
The California Penal Code goes into effect.
January 17 – American Indian Wars: The First Battle of the Stronghold is fought during the Modoca War.
February 11 – The Spanish Cortes deposes King Amadeus I and proclaims the First Spanish Republic.
Emilio Castelar, the former foreign minister, becomes prime minister of the new Spanish Republic.
The Coinage Act of 1873 in the United States is signed into law by president Ulysses S. Grant; coming into effect on April 1 it ends bimetallism in the U.S. and places the country on the gold standard.
February 20 – The University of California opens its first medical school in San Francisco.
February 20 – British Naval Officer John Morseby discovers the site of Port Moresby and claims the land for Britain.
March 3 – Censorship: The United States Congress enacts the Comstock Law, making it illegal to send any "obscene, lewd, or lascivious" books through the mail.
March 4 – Ulysses S. Grant is sworn in for a second term as President of the United States.
March 15 – The Phi Sigma Kappa fraternity is founded at the Massachusetts Agricultural College.
March 19 – German Modernist composer Max Reger is born in Brand, Bavaria.
March 22 – Emancipation Day for Puerto Rico: Slaves are freed (with a few exceptions).
March 29 – The Rio Tinto Company is formed in Spain, following the February 17 purchase of the Rio Tinto mine from the Spanish government by a British investment group.
April 1 – The British steamer RMS Atlantic sinks off Nova Scotia, killing 547.
April 4 – The Kennel Club, the world's first kennel club, is founded in the United Kingdom.
April 15–17 – American Indian Wars: The Second Battle of the Stronghold is fought.
April 19 – 11 perish in a train derailment due to a bridge washout in the village of Richmond Switch (now Wood River Junction) in Richmond, Rhode Island.
May – Henry Rose exhibits barbed wire at an Illinois county fair, which is taken up by Joseph Glidden and Jacob Haish, who invent a machine to mass-produce it.
May 5 – Battle of Eraul: Carlists under General Dorregaray defeat Republicans at Eraul, near Estella during the Third Carlist War.
Der Gründerkrach: The Wiener Börse (Vienna stock exchange) crash in Austria-Hungary ends the Gründerzeit and heralds the global Panic of 1873 and Long Depression.
The Battle of Montejurra at Navarra, Spain, is fought during the Third Carlist War.
Levi Strauss and Jacob Davis receive United States patent#139121 for using copper rivets to strengthen the pockets of denim work pants. Levi Strauss & Co. begin manufacturing the famous Levi's brand of jeans, using fabric from the Amoskeag Manufacturing Company in Manchester, New Hampshire.
In Chipping Norton, England, rioters attempt to free the Ascott Martyrs –sixteen women sentenced to imprisonment for attempting to dissuade strikebreakers.
The Canadian Parliament establishes the North-West Mounted Police (which is renamed the Royal Canadian Mounted Police in 1920).
The Preakness Stakes horse race is run for the first time in Baltimore.
Classical archaeologist Heinrich Schliemann discovers Priam's Treasure.
C. Laan brings order to the chaos created by the dockworker riots of Tripoli, Lebanon.
The city of Khiva falls to Imperial Russian forces, under the command of General Konstantin von Kaufman.
June 4 – American Indian Wars: The Modoc War ends with the capture of Kintpuash ("Captain Jack").
June 9 – Alexandra Palace in London is destroyed by fire only a fortnight after its opening.
July – The end of the war between the United Kingdom and Ghana's King Kofi KariKari, who is involved in the trading of slaves leads to the establishment of the Gold Coast Colony.
July 1 – Prince Edward Island joins the Canadian Confederation.
July 9 – Battle of Alpens (Third Carlist War): Campaigning in Catalonia, a government column under General José Cabrinety is ambushed at Alpens, 15 miles east of Berga, by Carlist forces under General Francisco Savalls. After heavy fighting, with Cabrinety killed, virtually the entire column of 800 men is killed or captured.
July 21 – At Adair, Iowa, Jesse James and the James–Younger Gang pull off the first successful train robbery in the American Old West (US$3,000 from the Rock Island Express).
August 4 – American Indian Wars: While protecting a railroad survey party in Montana, the Seventh Cavalry, under Lieutenant Colonel George Armstrong Custer, clashes for the first time with the Sioux, near the Tongue River (only 1 man on each side is killed).
August 12 – A peace treaty is signed between Imperial Russia and the Khanate of Khiva, making the khanate a Russian protectorate.
August 30 – The Austro-Hungarian North Pole Expedition discovers Franz Josef Land.
September 15 – Agreement for establishment of the International Meteorological Organization (IMO).
September 16 – German troops leave France upon completion of payment of indemnity for the Franco-Prussian War.
September 17 – The Ohio Agricultural and Mechanical College, later Ohio State University, opens its doors with 25 students, including 2 women.
September 18 – The New York stock market crash triggers the Panic of 1873, part of the Long Depression.
September 25 – Classes begin at Drury University in Springfield, Missouri, USA.
October – Beginning of the Long Depression
The County Carlow Football Club (Rugby union) is founded in Ireland.
Battle of Mañeru (Third Carlist War): In continued campaigning in Navarre, Spanish Republican General Domingo Moriones meets a Carlist force under Nicolás Ollo at Mañeru, near Puente de la Reina, in a hard-fought but indecisive action. While both sides claim victory, the Carlists are said to have had the advantage, and a month later Moriones is repulsed in a costly assault further west against Estella
November 6 – The Halifax rugby league club is founded.
Alexander Mackenzie becomes the second Prime Minister of Canada.
Battle of Montejurra (Third Carlist War): Determined to recapture the key city of Estella in Navarre, Spanish Republican General Domingo Moriones advances on the Carlists under General Joaquín Elío at nearby Montejurra. After very heavy fighting both sides claim victory, but Moriones withdraws and Estella remains in Carlist hands. Don Carlos is present in the front line.
November 17 – Budapest, Hungary's capital, is formed from Pest, Buda and Óbuda.
November 18–21 – Irish Home Rule movement: The Home Government Association reconstitutes itself as the Home Rule League.
December – Major Walter Clopton Wingfield designs and patents a racquet sport which he calls sphairistike (Greek σφάίρίστική, "skill at playing at ball"), soon known simply as Stické, for the amusement of his guests at a garden party on his estate of Nantclwyd, in Llanelidan, Wales.
December 15 – Women of Fredonia, New York, march against the retail liquor dealers in town to inaugurate the Woman's Crusade of 1873–74. This leads to the creation of the Woman's Christian Temperance Union (December 23) in Hillsboro, Ohio.
December 16 – The Heineken Brewery is founded in Amsterdam, the Netherlands.
December 21 – Francis Garnier is attacked outside Hanoi by Black Flag mercenaries fighting for the Vietnamese.
December 22 – Battle of Bocairente (Third Carlist War): Campaigning in Valenica, Spanish Republican General Valeriano Weyler is attacked at Bocairente, northwest of Alcoy, by a greatly superior Carlist force under General José Santés. Weyler was initially driven back, losing some of his guns, but in a brilliant counter-attack he turns defeat into victory and Santés is heavily repulsed and forced to withdraw.
December 23 – The Woman's Christian Temperance Union is founded, in Hillsboro, Ohio, USA.
December 27 – Siege of Bilbao (Third Carlist War; until 2 May 1874): Campaigning in Navarre, Pretender Don Carlos VII and General Joaquín Elío besiege Bilbao, held by General Ignacio del Castillo and 1,200 men. The Carlist force is ten times this number and includes most of the troops from Navarre, Vizcaya and Álava, although a considerable force is left in Guipúzcoa. Despite defeat at nearby Somorrostro, Republic commander Marshal Francisco Serrano, supported by Generals Manuel de la Concha and Arsenio Martínez-Campos, brilliantly breaks the siege and Concha then marches on Estella.
League of the Three Emperors is created. It links the conservative monarchs of Austria-Hungary, Germany and Russia in an alliance against radical movements.
Toronto Argonauts, the oldest professional sports team still playing in North America.
Royal Montreal Club in Montreal, the first permanent golf club in North America.
Liebig's Extract of Meat Company begin producing tinned corned beef, sold under the label Fray Bentos from the town in Uruguay where it is processed.
Coors Brewing Company begins making beer in Golden, Colorado.
The Swedish arms company Aktiebolaget (AB) Bofors-Gullspång is founded, better known as Bofors.
DDT is first synthesized.
In Mexico, the Veracruz to Mexico City railroad is completed.
Pyotr Ilyich Tchaikovsky composes The Tempest.
Nine Pekin ducks are imported to Long Island (the first in the United States).
The Married Woman's Property Rights Association is founded in Sweden.
January 2 – Saint Thérèse of Lisieux, Catholic saint and mystic (d. 1897)
January 4 – Blanche Walsh, stage & screen actress (d. 1915)
January 7 – Adolph Zukor, Austrian-born film studio pioneer (d. 1976)
Iuliu Maniu, Romanian politician (d. 1953)
Grace Van Studdiford, American stage actress & opera singer (d. 1927)
January 9 – Thomas Curtis, American athlete (d. 1944)
January 10 – George Orton, Canadian athlete (d. 1958)
January 12 – Spyridon Louis, Greek runner (d. 1940)
January 20 – Johannes V. Jensen, Danish writer, Nobel Prize laureate (d. 1950)
January 28 – Colette, French writer (d. 1954)
January 29 – Prince Luigi Amedeo, Duke of the Abruzzi, Italian mountaineer, explorer, and admiral (d. 1933)
January 30 – Vassily Balabanov, an administrator and Provincial Governor of Imperial Russia (d. 1947)
January 31 – Melitta Bentz, German entrepreneur, who invented the coffee filter in 1908 (d. 1950)
February 2 – Maurice Tourneur, French film director (d. 1961)
Hugh Trenchard, British military aviation pioneer (d. 1956)
Karl Jatho, German aviation pioneer (d. 1933)
Étienne Desmarteau, Canadian athlete (d. 1905)
Joel R. P. Pringle, American admiral (d. 1932)
February 7 – Thomas Andrews, Irish shipbuilder (d. 1912)
February 13 – Feodor Chaliapin, Russian bass opera singer (d. 1938)
February 15 – Hans von Euler-Chelpin, German-born chemist, Nobel Prize laureate (d. 1964)
February 19 – Louis Feuillade, French film director (d. 1925)
February 25 – Enrico Caruso, Italian tenor (d. 1921)
March 3 – William Green, American labor leader (d. 1952)
March 8 – Anna Held, French actress, (d. 1918)
March 11 – David Horsley, English-born film executive (d. 1933)
March 13 – Léon Delagrange, French sculptor & pioneer aviator (d. 1910)
March 19 – Max Reger, German composer (d. 1916)
April 1 (N.S.)/March 20 (O.S.) – Sergei Rachmaninoff, Russian composer and pianist (d. 1943)
April 7 – John McGraw, baseball player and manager (d. 1934)
April 10 – Kyösti Kallio, Prime Minister and President of Finland (d. 1940)
Ingeborg Rönnblad, Swedish actress
Sydney Barnes, English cricketer (d. 1967)
April 20 – Gombojab Tsybikov, Russian explorer (d. 1930)
April 22 – Ellen Glasgow, American writer (d. 1945)
April 23 – Theodor Körner, President of Austria (d. 1957)
Walter de la Mare, English poet, short story writer and novelist (d. 1956)
Félix d'Herelle, French-Canadian microbiologist (d. 1949)
May – Leon Czolgosz, assassin of U.S. President William McKinley (d. 1901)
May 4 – Joe De Grasse, Canadian film director (d. 1940)
May 9 – Anton Cermak, Mayor of Chicago (d. 1933)
Henri Barbusse, French novelist and journalist (d. 1935)
Dorothy Richardson, English feminist writer (d. 1957)
May 18 – Lucy Beaumont, English actress (d. 1937)
May 21 – Hans Berger, German neurologist (d. 1941)
May 28 – D. D. Sheehan, Irish politician (d. 1948)
June 3 – Otto Loewi, German-born pharmacologist, recipient of the Nobel Prize in Physiology or Medicine (d. 1961)
June 26 – Alexis Carrel, French surgeon and biologist, recipient of the Nobel Prize in Physiology or Medicine (d. 1944)
July 1 – Alice Guy-Blaché, French-American filmmaker (d. 1968)
July 3 – Prince Yamashina Kikumaro, Japanese Prince (d. 1908)
July 6 – Dimitrios Maximos, Prime Minister of Greece (d. 1955)
July 20 – Alberto Santos-Dumont, Brazilian aviation pioneer (suicide 1932)
July 21 – Walter Morley Fletcher, British physiologist and administrator (d. 1933)
August 5 – Joseph Russell Knowland, American politician and newspaperman (d. 1966)
August 13 – Cornelis Jacobus Langenhoven, South African author (d. 1932)
August 17 – John A. Sampson, American gynecologist (d. 1946)
August 25 – Blanche Bates, actress (d. 1941)
August 26 – Lee de Forest, American inventor (d. 1961)
September 1 – Sir Guy Standing, British actor (d. 1937)
Felicija Bortkevičienė, Lithuanian politician and publisher (d. 1945)
September 5 – Cornelius Vanderbilt III, American military officer, inventor, engineer (d. 1942)
September 8 – David O. McKay, president of The Church of Jesus Christ of Latter-day Saints (d. 1970)
Sidney Olcott, pioneer film director (d. 1949)
Ferenc Szisz, Hungarian-born race car driver (d. 1944)
September 21 – Papa Jack Laine, jazz musician (d. 1966)
September 25 – Fawcet Wray, British admiral (d. 1932)
September 26 – Wacław Berent, Polish novelist and translator (d. 1940)
October 2 – Stephen Warfield Gambrill, U.S. Congressman for Maryland's 5th District (d. 1924)
October 3 – Emily Post, American etiquette expert (d. 1960)
October 8 – Ma Barker, American criminal (d. 1935)
Charles Rudolph Walgreen, American businessman (d. 1939)
Karl Schwarzschild, German physicist and astronomer (d. 1916)
October 14 – Ray Ewry, American athlete (d. 1937)
October 18 – Harris Laning, American admiral (d. 1941)
Jaap Eden, Dutch skater and cyclist (d. 1925)
John Barton King, American cricketer (d. 1965)
Thorvald Stauning, Prime Minister of Denmark (d. 1942)
A. K. Fazlul Huq, Bengali statesman (d. 1962)
November 9 – Fritz Thyssen, German industrialist (d. 1951)
November 16 – W. C. Handy, American blues composer (d. 1958)
November 22 – Johnny Tyldesley, English cricketer (d. 1930)
November 28 – Frank Phillips, American oil executive (d. 1950)
December 7 – Willa Cather, American novelist (d. 1947)
December 11 – Josip Plemelj, Slovenian mathematician (d. 1967)
December 17 – Ford Madox Ford, English writer (d. 1939)
December 20 – Kan'ichi Asakawa, Japanese historian(d. 1948)
December 26 – Thomas Wass, Nottinghamshire bowler (d. 1953)
Al Smith, American politician (d. 1944)
Phillip Linnington born to the Linnington Family. (d. 1873)
Thomas Chrostwaite, American educator (d. 1958)
James Cousins, Irish writer (d. 1956)
William Ernest Hocking, American philosopher (d. 1966)
January 9 – Napoleon III, last Emperor of the French (b. 1808)
January 18 – Edward Bulwer-Lytton, English novelist (b. 1803)
January 20 – The Venerable Father Basil Anthony Marie Moreau, French founder of the Congregation of Holy Cross (b. 1799)
January 23 – Ramalinga Swamigal, Hindu religious leader (b. 1823)
January 26 – Empress Amélie, consort of Pedro I of Brazil (b. 1812)
February 3 – Isaac Baker Brown, English gynaecologist and surgeon (b. 1811)
February 7 – Sheridan Le Fanu, Irish writer (b. 1814)
February 19 – Vasil Levski, Bulgarian revolutionary, executed (b. 1837)
March 10 – John Torrey, American botanist (b. 1796)
March 24 – Mary Ann Cotton, English serial killer, executed (b. 1832)
March 25 – Wilhelm Marstrand, Danish painter (b. 1810)
March 29 – Prince Unakan Ananta Norajaya Prince of Siam (b. 1856)
March 31 – Hugh Maxwell, American lawyer and politician (b. 1787)
April 11 – Edward Canby, American general (b. 1817)
April 18 – Justus von Liebig, German chemist (b. 1803)
April 27 – William Charles Macready, English actor (b. 1793)
May 1 – David Livingstone, Scottish explorer of Africa (b. 1813)
May 6 – José Antonio Páez, first President of Venezuela (b. 1790)
May 7 – Salmon P. Chase, Chief Justice of the United States (b. 1808)
May 8 – John Stuart Mill, British philosopher (b. 1806)
May 15 – Alexandru Ioan Cuza, first ruler of Romania (b. 1820)
May 20 – George-Étienne Cartier, Canadian statesman (b. 1814)
May 29 – Édouard de Verneuil, French palaeontologist (b. 1805)
June 1 – Joseph Howe, Canadian politician (b. 1804)
August 18 – Charles II, Duke of Brunswick (b. 1804)
September 11 – Agustín Fernando Muñoz, 1st Duke of Riánsares, morganatic husband of Maria Christina of the Two Sicilies (b. 1808)
September 17 – Alexander Berry, Scottish adventurer and Australian pioneer (b. 1781)
September 22 – Friedrich Frey-Herosé, Swiss Federal Councilor (b. 1801)
September 23 – Jean Chacornac, French astronomer (b. 1823)
October 5 – William Todd, American businessman, Canadian senate nominee (b. 1803)
October 9 – George Ormerod, English historian and antiquarian (b. 1785)
November 8 – Manuel Bretón de los Herreros, Spanish playwright (b. 1796)
Louis Agassiz, Swiss-born geologist and naturalist (b. 1807)
Alexander Keith, Scottish-born brewer and mayor of Halifax, Nova Scotia (b. 1795)
The 2011 western movie Cowboys & Aliens is set in 1873.
There is some debate about whether The Pirates of Penzance is set in 1873 or 1877.
1873 (MDCCCLXXIII) was a common year starting on Wednesday (dominical letter E) of the Gregorian calendar and a common year starting on Monday (dominical letter G) of the Julian calendar, the 1873rd year of the Common Era (CE) and Anno Domini (AD) designations, the 873rd year of the 2nd millennium, the 73rd year of the 19th century, and the 4th year of the 1870s decade. As of the start of 1873, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.