Born in Vienna, he was the younger brother of stage director Ernst Lert.
After graduating with a music degree from the University of Vienna, he took a conducting post at the Opernhaus Düsseldorf in 1910.
In 1916 he married harpist Vicki Baum (who later became a well-known novelist) and that same year joined the conducting staff of the Opern- und Schauspielhaus Frankfurt.
In 1947 he co-founded the Music Academy of the West in Montecito, California, serving on the faculty there for many years.
His papers are held in the collection at the library of the University of Southern California where he was also a faculty member.