January 2 - Russo-Japanese War: The Russian garrison surrenders at Port Arthur, China.
January 2 - The American anarcho-syndicalist union known as the Industrial Workers of the World forms.
January 9 - According to the Julian Calendar which was used at the time, Russian workers stage a march on the Winter Palace that ends in the massacre by Tsarist troops known as Bloody Sunday, setting off the Russian Revolution of 1905.
January 22 - Bloody Sunday in St. Petersburg, beginning of the 1905 revolution.
January 26 - The Cullinan Diamond is found near Pretoria, South Africa at the Premier Mine.
February 23 - Chicago attorney Paul Harris and three other businessmen meet for lunch to form the Rotary Club, the world's first service club.
March 3 - Tsar Nicholas II of Russia agrees to create an elected assembly (the Duma).
March 5 - Russian troops begin to retreat from Mukden, Manchuria after losing 100,000 troops in three days.
March 10 - Eleftherios Venizelos asks the independence of Crete and its union with Greece again, starting the Cretan Revolution in Theriso.
April 4 - In India, an earthquake near Kangra kills 20,000.
April 11 - Albert Einstein reveals his Theory of Relativity (special relativity).
April 17 - The Supreme Court of the United States decides Lochner v. New York which held that the "right to free contract" was implicit in the due process clause of the Fourteenth Amendment of the United States Constitution.
May 15 - Las Vegas, Nevada, is founded when 110 acres (0.4 km²), in what later would become downtown, are auctioned off.
May 27 - Russo-Japanese War: The Battle of Tsushima begins.
May 28 - Russo-Japanese War: the Battle of Tsushima ends with the destruction of the Russian Baltic Fleet by Admiral Togo Heihachiro and the Imperial Japanese Navy.
June 7 - Norway's parliament dissolves its union with Sweden, a vote that was confirmed by a national plebiscite on August 13 of that year.
June 27 - (June 14 according to the Julian calendar): Battleship Potemkin uprising: sailors start a mutiny aboard the Battleship Potemkin, denouncing the crimes of autocracy, demanding liberty and an end to war.
June 30 - Albert Einstein publishes the article "On the Electrodynamics of Moving Bodies", in which he introduces special relativity.
July 6 - Alfred Deakin becomes Prime Minister of Australia for the second time.
August 10 - Russo-Japanese War: Russian and Japanese peace negotiations begin in Portsmouth.
September 1 - Alberta and Saskatchewan join the Canadian confederation.
September 5 - Russo-Japanese War: In New Hampshire, USA, the Treaty of Portsmouth, mediated by US President Theodore Roosevelt, ends the war.
September 23 - Norway and Sweden sign the "Karlstad treaty", peacefully dissolving the Union between the two countries.
September 27 - The physics journal Annalen der Physik published Albert Einstein's paper "Does the Inertia of a Body Depend Upon Its Energy Content?", introducing the equation E=mc².
October 1 - František Pavlík is killed in a demonstration in Prague, inspiring Leoš Janáček to the piano composition 1. X. 1905.
October 5 - Wilbur Wright pilots Wright Flyer III in a flight of 24 miles in 39 minutes, a world record that stood until 1908.
October 16 - The Partition of Bengal in India takes place.
October 26 - Norway becomes independent from Sweden.
October 30 - Czar Nicholas II of Russia grants Russia's first constitution, creating a legislative assembly.
November 3 - Czar Nicholas II of Russia signs a document of amnesty for the political prisoners.
November 12 - (November 12 & November 13) Norway holds a referendum in favor of monarchy over republic.
November 17 - The Eulsa Treaty is signed between Japan and Korea.
November 21 - Albert Einstein's paper, "Does the Inertia of a Body Depend Upon Its Energy Content?", is published in the journal "Annalen der Physik". This paper reveals the relationship between energy and mass. This leads to the mass–energy equivalence formula E = mc².
November 25 - The Danish Prins Carl arrives in Norway to become King Haakon VII of Norway.
November 28 - Irish nationalist Arthur Griffith founds Sinn Féin as a political party with the main aim of establishing a dual monarchy in Ireland.
December 9 - In France, the law separating church and state is passed.
December 11 - A workers uprising occurs, establishing the Shuliavka Republic in Kiev.
December 15 - The Pushkin House is established in St. Petersburg to preserve the cultural heritage of Alexander Pushkin
December 30 - Former Governor Frank Steunenberg is assassinated near his home in Caldwell, Idaho.