[2] He also shifted his scholarly interests to historical musicology, eventually becoming music librarian, working in the archives of Anthony van Hoboken.

[2] In 1938, when Austria was taken over by Nazi Germany in the Anschluss, Deutsch decided to flee the country, as he was a Protestant of Jewish origin.

Deutsch was a close friend of music theorist Heinrich Schenker,[3] and of the British musicologist and Schubert scholar Maurice J. E.

According to David Wyn Jones, Deutsch's work was based on "an abiding belief that historical documents and iconographic[5] evidence constituted the essential ingredients of biographical exposition.

In these biographies, Deutsch lets the documents speak for themselves, with his supplementary remarks providing clarifications, corrections, and context.