Genocide has occurred throughout history, but the crime of genocide was only recognized in international law after the Second World War. The term genocide was first coined by Raphael Lemkin in 1944 stemming from the word 'genos', meaning 'race, nation or tribe' in ancient Greek, and 'caedere', meaning 'to kill' in Latin. Lemkin’s definition of genocide was in some respects broader than the one later endorsed in the Genocide Convention since it was not limited to the physical destruction of a group, but also included acts aimed at destroying the culture and livelihood of the group. However, this broad conception was rejected during the political negotiations that resulted in the Convention, due in part to the concern (by the drafting states) that they themselves may be censured for their own historical crimes, suppression of political opponents, and colonial records.

The international crime of genocide was not recognized as such at the International Military Tribunal (IMT) in Nuremberg created in 1945; which dealt with the trial of the leading Nazi war criminals. Following from the Nuremberg Charter, the IMT’s mandate included those atrocities that were categorized as "crimes against humanity", which were defined as "murder, extermination, enslavement, and other inhumane acts committed against any civilian population […] on political, racial, or religious grounds". The scope of those crimes was limited since they had to be committed in association with the waging of an aggressive war. As a consequence, no Nazis were convicted at Nuremberg for any of the crimes committed before the outbreak of the war, such as the 1938 Kristallnacht. Nevertheless, reference to genocide was made during the trial, charging the defendants with "deliberate and systematic genocide, viz., the extermination of racial and national groups, […] in order to destroy particular races and classes of people, and national, racial or religious groups, particularly Jews, Poles and Gypsies." The final judgment in the trial of the major war criminals never used the term genocide, but described at length what it entailed.

Immediately after the final judgment of the IMT in October 1946, Cuba, India, and Panama submitted a draft resolution to the United Nations General Assembly with the purpose of genocide being recognized as an international crime. This was to correct a major shortcoming of the Nuremberg Tribunal, which had precluded the punishment of certain crimes of genocide, since they had been committed before the war, and therefore remained unpunished. The Resolution on the Crime of Genocide was unanimously adopted by the General Assembly on 11 December 1946.

Two years later in 1948, the General Assembly adopted the Convention on the Prevention and Punishment of the Crime of Genocide as the first treaty in the United Nations system to address the prevention of genocide and mass killing. Unlike the Nuremberg Charter, the Convention recognizes genocide as an international crime, not just in connection to armed conflict, but also in time of peace (Article 1) and sets out obligations upon contracting parties with regards to prosecution and extradition.