January 1, 1873 – Japan begins using the Gregorian calendar.

January 17, 1873 – A group of Modoc warriors defeats the United States Army in the First Battle of the Stronghold, a part of the Modoc War.

April 1, 1873 – The British steamer RMS Atlantic sinks off Nova Scotia, killing 547.

April 13, 1873 – The Colfax Massacre takes place.

July 1, 1873 – Prince Edward Island joins the Canadian Confederation.

July 21, 1873 – At Adair, Iowa, Jesse James and the James-Younger Gang pull off the first successful train robbery in the American Old West.

August 4, 1873 – Indian Wars: whilst protecting a railroad survey party in Montana, the United States 7th Cavalry, under Lieutenant Colonel George Armstrong Custer clashes for the first time with the Sioux near the Tongue River; only one man on each side is killed.

August 30, 1873 – Austrian explorers Julius von Payer and Karl Weyprecht discover the archipelago of Franz Joseph Land in the Arctic Sea.

September 15, 1873 – Franco-Prussian War: The last German troops leave France upon completion of payment of indemnity.

October 9, 1873 – A meeting at the U.S. Naval Academy establishes the U.S. Naval Institute.

January 7, 1873 – Charles Péguy, French poet and essayist (d. 1914)

January 8, 1873 – Elena of Montenegro, queen of Italy (d. 1956)

January 20, 1873 – Johannes Vilhelm Jensen, Danish Nobel laureate (d. 1950)

February 13, 1873 – Feodor Chaliapin, Russian bass (d. 1938)

April 7, 1873 – John McGraw, American baseball player and manager (d. 1934)

September 13, 1873 – Constantin Carathéodory, Greek mathematician (d. 1950)

September 21, 1873 – Papa Jack Laine, American musician (d. 1966)

October 9, 1873 – Karl Schwarzschild, German physicist and astronomer (d. 1916)

October 19, 1873 – Jaap Eden, Dutch skater and cyclist (d. 1925)

November 10, 1873 – Henri Rabaud, French composer and conductor (d. 1949)