He starred in the original 1928 production of Bertolt Brecht's The Threepenny Opera, as well as the subsequent 1931 film by Georg Wilhelm Pabst.

[5] Eva settled in Paris while Ernst initially made his home in the Soviet Union where he worked with Gustav von Wangenheim on the 1935 film "Kämpfer" ("Fighters").

After the Spanish Republic fell to General Franco, Busch migrated to Belgium where he was interned during the German occupation and later imprisoned in Camp Gurs, France and Berlin.

Freed by the Red Army in 1945, he settled in East Berlin, where he acted in the first play to be produced in the American-occupied zone, Robert Ardrey's Thunder Rock.

A beloved figure in the German Democratic Republic, he is best remembered for his performance in the title role of Brecht's Life of Galileo and his recordings of workers songs, including many written by Hanns Eisler.