Kaschdan came from a Moscow merchant family. He graduated from a teacher training college in the city of Ufa and worked from 1956 at the Institute for the History of the Soviet Academy of Sciences. There he was, among others, the author of several translations of ancient and medieval works as well as of scientific publications on Byzantine history.
1978 emigrated with his family Kaschdan first to Israel, then to the United States. There he worked among other things as a lecturer at Princeton University. In the Soviet Union after Kaschdans emigration were his previous publications largely withdrawn from circulation.
He is the father of the mathematician David Kazhdan.