He spent his twenties working backstage and in smaller roles, before achieving his breakthrough in 1902 in Franz Lehár's Der Rastelbinder [de] opposite Mizzi Günther.
In 1905 he created the role of Count Danilo Danilovitsch in Lehár's Die lustige Witwe (The Merry Widow).
During the second half of the 1920s he appeared in several silent films, such as Der Rastelbinder (1927), Flucht in die Fremdenlegion (1929), Spiel um den Mann (1929), Trust der Diebe (1929), Katharina Knie (1929) and Die Warschauer Zitadelle (1930).
He was repeatedly scheduled for transport to a concentration camp, each time saved by influential friends such as Franz Lehár.
However on 28 July 1942, aged 70 years old, Treumann was finally deported to Theresienstadt together with his wife Stefanie.