In June 1946, within a year of the termination of fighting in WWII, he arranged for an international meeting of crystallographers in London which was attended by some 120 scientists from most of the allied countries. In that London meeting Ewald was elected Chairman of the Provisional International Crystallographic Committee, which put into action the decision to form the International Union of Crystallography.
Following World War II, just a year later, he organized an international symposium on crystallography in London that drew about 120 scientists from most of the Allied countries. It was at this gathering that Ewald was chosen as the chairman of the Provisional International Crystallographic Committee, which subsequently led to the formation of the International Union of Crystallography.