He got into film production through his father Heinrich Nebenzahl (1870–1938), who, in the early 1920s, worked with German action star Harry Piel.
As head of this company Seymour Nebenzal became one of the most important producers of the transition period from silent to sound film in Germany.
He worked with the directors Georg Wilhelm Pabst, Arthur Ripley, Douglas Sirk, Harold S. Bucquet, Edgar G. Ulmer, Léonide Moguy, Paul Czinner and Fritz Lang among others.
[3] In Paris he produced films by other exiles from Germany such as his cousin Robert Siodmak and Max Ophüls as well as Anatole Litvak, Fedor Ozep, and Raymond Bernard.
Harold became a script writer (The Wilby Conspiracy), film producer (Cabaret, Gabriela) and novelist (Cafe Berlin).