1912 (MCMXII) was a leap year starting on Monday in the Gregorian calendar and a leap year starting on Sunday in the Julian calendar.

• January 1 – Establishment of Republic of China.
• January 5 – Prague Party Conference
• January 6 – New Mexico is admitted as the 47th U.S. state.
• January 17 – British polar explorer Robert Falcon Scott and a team of four begin the second expedition to reach the South Pole.
• January 23 – The International Opium Convention is signed at The Hague.
• February 8 – Mexican Revolution – Military rebellion against the rule of Francisco Madero begins in Mexico City. Battles last for 10 days
• February 12 – Republic of China adopts the Gregorian calendar
• February 14 – Arizona is admitted as the 48th U.S. state.
• February 14 – In Groton, Connecticut, the first diesel-powered submarine is commissioned.
• February 18 – Francisco Madero is forced to resign – battle ends. All members of Madero's government are arrested.
• February 19 – Prizes are included in Cracker Jack candy boxes for the first time
• February 22 – Francisco Madero and Pino Suarez are shot, allegedly when they "tried to escape"
• March 1 – Albert Berry makes the first parachute jump from a moving airplane.
• March 1 – Georg Ritter von Trapp, head of the famous Austrian singing family memorialized in the musical The Sound of Music marries Agathe
• March 5 – Italian forces are the first to use airships for a military purpose by using them for reconnaissance west of Tripoli behind Turkish lines.
• March 7 – Roald Amundsen announces discovery of the South Pole
• March 7 – French aviator Henri Seimet makes the first non-stop flight from Paris to London in three hours
• March 12 – The Girl Guides (later renamed the Girl Scouts) are founded.
• March 16 – Lawrence Oates, ill member of Scott's South Pole expedition leaves the tent saying, "I am just going outside and may be some time"
• March 27 – Mayor Yukio Ozaki of Tokyo gives 3,000 cherry blossom trees to be planted in Washington, D.C. to symbolize the friendship between the two countries.
• March 30 – France establishes a protectorate over Morocco.
• April 14–15 – The R.M.S Titanic sank after hitting an iceberg in the middle of the Atlantic Ocean. Over 1500 people died.
• April 20 – Fenway Park opens in Boston, Massachusetts. The Red Sox defeat the New York Highlanders 7-6 in 11 innings in the first game. It is the oldest active ballpark.
• Alexis Carrel, French surgeon, won the 1912 Nobel Prize in Physiology or Medicine

• January 8 – José Ferrer, Puerto Rican actor and theatre and film director (d. 1992)
• January 28 – Jackson Pollack, American artist (d. 1956)

• February 19 – Anton Buttigieg, 2nd President of Malta (d. 1983)

• March 5 – Jack Marshall, Prime Minister of New Zealand (d. 1988)
• March 12 – Pat Nixon, 39th First Lady of the United States (d. 1993)
• March 22 – Karl Malden, American actor (d. 2009)
• March 27 — James Callaghan, Prime Minister of the United Kingdom (d. 2005)

• April 8 – Sonja Henie, Norwegian figure skater (d. 1969)
• April 15 – Kim Il-sung, Supreme Leader of North Korea (d. 1994)

• May 9 – Pedro Armendáriz, Mexican actor (d. 1963)

• June 23 – Alan Turing, English mathematician (d. 1954)

• August 13 – Salvador Luria, Italian American microbiologist (d. 1991)
• August 23 – Gene Kelly, American dancer, actor, singer, director, producer and choreographer (d. 1996)
• August 25 – Erich Honecker, East German leader (d. 1994)

• September 5 – John Cage, American composer (d. 1992)
• September 21 – Chuck Jones, American animator, cartoon artist, screenwriter, producer, and director of animated films (d. 2002)

• October 7 – Fernando Belaúnde Terry, 49th and 52nd President of Peru (d. 2002)
• October 17 – Pope John Paul I (d. 1978)

• December 2 – Boun Oum, 4th Prime Minister of Laos (d. 1980)
• December 22 – Lady Bird Johnson, 38th First Lady of the United States (d. 2007)

• February 12 – Gerhard Armauer Hansen, Norwegian doctor and scientist (b. 1841)
• May 30 – Wilbur Wright of the Wright brothers, American co-inventor of the airplane.
• April 15 – Over 1500 people die on the R.M.S Titanic
• December 11 - James Otis, American children's writer

• May 29 - Premiere of Nijinsky's ballet The Afternoon of a Faun in Paris