The IRO assumed most of the functions of the earlier United Nations Relief and Rehabilitation Administration.

In 1952, operations of the IRO ceased, and it was replaced by the Office of the United Nations High Commissioner for Refugees (UNHCR).

The Constitution of the International Refugee Organization, adopted by the United Nations General Assembly on 15 December 1946, is the founding document of the IRO.

[2] Twenty-six states became members of the IRO and it formally came into existence in 1948: Argentina, Australia, Belgium, Bolivia, Brazil, Canada, Republic of China, Chile, Denmark, the Dominican Republic, France, Guatemala, Honduras, Iceland, Italy, Liberia, Luxembourg, the Netherlands, New Zealand, Norway, Panama, Peru, the Philippines, Switzerland, the United Kingdom, the United States, and Venezuela.

Of particular importance was the Office of the High Commissioner for Refugees, established in January 1951 as a part of the United Nations, and the Intergovernmental Committee for European Migration (originally PICMME), set up in December 1951.