In 1944, Blumental joined the Central Jewish Historical Commission in Poland. In 1947, he became the main expert of the prosecution in the trial against the commandant of Auschwitz, Rudolf Höß. In the same year, Blumental was named the first director of the Jewish Historical Institute in Warsaw. He edited a dictionary of terms used by the Germans in ghettos and concentration camps.
In 1950, Blumental emigrated to Israel, where he published the two most influential journals on the Holocaust: Dapim leḥeker hashoah vehamered (Pages for Research of the Holocaust and Resistance) and the Bulletin of the State Memorial Yad Vashem. The political prerogative of his Holocaust research was important to him.