Ernst was one of five sons born to a Jewish family in the Prussian city of Koenigsberg. He studied pharmacy and earned his doctorate in the late 1880s. Ernst spent several years as an apprentice before buying his own pharmacy in Berlin. Later, he also acquired a pharmaceuticals factory and supplied oxygen to hospitals. He married Marta Friedberg and the couple raised two sons.
1933-39: In Berlin, Ernst and his family lived in an apartment above their pharmacy and factory. In 1938 Ernst was forced to sell his business [Aryanization] for well below its market value to an "Aryan" German. Soon after, fearing the Nazis, Ernst's son Fritz and his family left for Amsterdam. A year later, Ernst sent his wife, Marta, to Amsterdam, where she joined Fritz and his family. Ernst decided to remain in Berlin.
1940-43: Ernst was able to eke out a living in the German capital with the financial assistance of former employees and non-Jewish friends with whom he had done business before the Nazis came to power. Despite warnings from these benefactors that he should hide to avoid deportation, Ernst refused. In 1943 Ernst received a notice that he was to be "relocated in the east," a Nazi euphemism for deportation.
On March 5, 1943, the Nazis arrested Ernst in his apartment. Rather than be deported, Ernst committed suicide.