Almost from the beginning of psychology as a modern science, international meetings of psychologists were organized to facilitate the exchange of ideas.

The first International Congress of Psychology was held in Paris in 1889, the second in London in 1892, the third in Munich in 1896, and the fourth in Paris in 1900. A continuing committee called the International Congress of Psychology was established to organize the successive congresses of psychology, and the Union grew out of this committee. Throughout the first half of the twentieth century, there was a growing sentiment that psychology should have an international organization with broader activities than arranging for the international congresses. After 1945 this coincided with an initiative of UNESCO to encourage the formation of international unions by sciences that did not already have one.

At the first International Congress of Psychology to be held after the second World War (Edinburgh, 1948), it was decided to organize an International Union of Psychological Science with statutes similar to those of international unions in the other sciences. Statutes were prepared, and they were adopted officially at the XIII International Congress of Psychology at Stockholm in 1951. At the same time, the International Congress committee turned over its functions to the Union. The last Secretary-General of the International Congress of Psychology committee, Prof. H. S. Langfeld, became the first Secretary-General of the Union, and some of the members of the International Congress committee were among the first officers and members of the Executive Committee of the Union. The Union is thus the direct successor to the International Congress committee, and its functions continue to expand.

Eleven charter member organizations founded IUPsyS on July 17, 1951 at the Stockholm International congress committee . Nine other National Members joined later that year. The further steady growth in membership testifies to the success of the Union.

As of 2005, there are 70. Their number will continue to grow; as applications are in various stages of preparation from candidate organizations in Africa, Asia, Eastern Europe, and South America.