[1] He initially worked as a theatre actor and served as a soldier in World War I, but had to leave military service early due to illness.
[2] He made his directorial debut in 1934 with the Karl Valentin short film Im Schallplattenladen and the comedy Da stimmt was nicht, with Viktor de Kowa and Adele Sandrock.
Zerlett's greatest success was the 1936 medical drama Arzt aus Leidenschaft and the 1938 revue film Es leuchten die Sterne, with La Jana.
During the following years he also made propaganda films, such as the anti-Semitic 1939 musical Robert und Bertram and the anti-'degenerate art' Venus vor Gericht (1941).
In the late 1930s Zerlett made friends with prominent sportsmen such as Gustav Jaenecke, Gottfried von Cramm, Rudolf Caracciola, Max Schmeling, along with the actor Hans Albers and the singer Michael Bohnen, who he used to meet regularly at the "Roxy-Sportbar" in Joachimstaler Straße in Berlin.