Having been educated in Prague and Berlin (where he studied under Julius Ruska), the rise of the Nazis in 1930s Germany forced him to move first to Paris and later to Cairo, where he died in 1944.
In 1933, with the Nazis coming to power in Germany and many Jews losing their jobs, Kraus left Berlin for Paris, where he was able to continue his studies under the French Orientalist Louis Massignon.
In 1935 he first published a French translation of Abu Bakr al-Razi's Philosophic Life,[6] following it in 1936 with a thesis on the work and importance of Jābir ibn Hayyān (whose name was latinized as Geber) to the science of chemistry.
In 1938 Kraus discovered the Al-Farabi manuscript (the philosophy of Plato and Aristotle and the Commentary on the Laws) in an Istanbul library, and notified his future brother-in-law, Leo Strauss, about it.
According to his Czech language biography, in a 1939 trip to Jerusalem, he regretted turning down the university position, since he discovered that the academic scene was completely changed, bustling with the top researchers of the field, and nothing to be compared with the time he had first been there in 1926.
At that time he was invited to a public debate held at the Hebrew University, where he set out his theory of the coherency of the Old Testament as a series of lyrics, perhaps as an oral tradition, which, he proposed, explained many inconsistencies and repeated parts in the texts.
Kraus's papers, which had been stored in the French Institute in Cairo and apparently plundered by other scholars, were finally brought to the United States by his daughter who donated them to the Special Collections Library of the University of Chicago.