After the Second World War, Cassin he became president of the Council of State (Conseil d’État), the highest administrative court in France, and was in charge of other high legal and administrative offices in France. Internationally, he helped found the United Nations Educational, Scientific and Cultural Organization (UNESCO) in 1944 and was a French delegate to UNESCO from 1945 to 1952. Representative of France to the UN from 1946 to 1968, He was chairman of the UN Commission on the Rights of Man (1947-1948) and helped draft the Universal Declaration of Human Rights. Even if Cassin was originally credited as the author of the document, an examination of the original manuscript seemed to indicate that it had been written by John Peters Humphrey, the director of the UN Human Rights division. From 1965 to 1968 Cassin was president of the European Court of Human Rights.
He received the Nobel Peace Prize on December 20, 1968, on the 20th anniversary of the ratification of the UN Declaration. In an article written on the occasion of the 1968 International Year for Human Rights, Cassin concludes with a simple warning: “Now that we have an instrument capable of lifting or alleviating the burden of oppression and injustice in the world, we have to learn to use it.“.
René Cassin He was also a Zionist and defender of the rights of the Jews; he was president of the Israelite Alliance in France. He died in Paris on February 20, 1976; his ashes are in the Pantheon in Paris.