Ernst Mayer was born in Bingen, Germany, where he took an apprenticeship in a banking house. He then worked in London and Paris before serving in the military during the First World War. During the 1920s he worked at the Rowohlt publishing house in Berlin and at the same time founded his own publishing house. The Mauritius Verlag initially published children's and art literature before specialising as a photo publisher.
During this time the demand for images and the network of photographers, photo agencies and illustrated magazines as well as publishing houses began to develop. Since the illustrated magazines could only afford a few staff photographers, photo agencies mediated between photographers and magazines. One of these agencies was Mauritius. On the side, Ernst Mayer began selling pictures by freelance photographers to the illustrated magazines, pursuing the strategy of selling entire reportage ideas. He suggested topics to magazine editors, even discussing the structure and layout of stories with them. Mauritius was commercially successful quite quickly and in 1929 Ernst Mayer travelled to the U.S. in a quest for material as there was a high demand for foreign images in Germany. With the seizure of power by the National Socialists in 1933, the art and photojournalism markets dried up and working as a Jew became almost impossible.
In 1922 Ernst Mayer married Helene Hirschberg (1894–1945) and they had two daughters, Regina (1926–2002) and Dorli (1931–1936). In Berlin, Ernst Mayer was in contact with Kurt Safranski, who worked at the Ullstein publishing house. Through Ernest Mayer’s mother, Mathilde Mayer (1869–1969), it is known that Kurt Kornfeld was also a friend of the Mayer family (Mayer 1991, 97). So Mayer, Kornfeld and Safranski already knew each other before they founded the Black Star Publishing Company in New York in 1936.

In 1935 Ernst Mayer worked for a short time in London but Kurt Safranski suggested that he move to New York. He made a visit the same year and decided to emigrate, which he did, arriving in New York in June 1935. Kurt Kornfeld moved to New York in 1936 and he and Ernst Mayer embarked on a plan to set up a new publishing house. Ernst Mayer sold his Mauritius publishing house to a Swiss photo agent in 1935 but was able to transfer part of his photo archive to New York. This provided a starting point for Black Star photo agency. Mayer's network of other German photographers who had emigrated to New York also helped him build the company. Kurt Safranski, who had been working at the Hearst Corporation, joined Mayer and Kurt Kornfeld in 1936 and became the third founding member of the Black Star Publishing Company. It was during this time that Ernst Mayer americanised his given name to Ernest.

As the demand for foreign and especially European images was high in the U.S., Black Star opened a branch in London's Fleet Street and for most of the time one of the three founders was based there. The London base allowed Ernest Mayer to meet his mother Mathilde Mayer and his brother Willy Mayer and it was from there that he also organised the emigration to New York of his wife Helene Mayer, in 1936, and of his mother, in 1937. During his first year in New York, from 1935 to 1936, Ernest resided at the Park Crescent Hotel at 150 Riverside Drive, where other German émigrés like Kurt Korff and Kurt Safranski had also lived and where he was joined in 1936 by Kurt Kornfeld. In 1936 Mayer and Kornfeld moved to a house at 30 Parcot Avenue, in New Rochelle, where already Kurt Safranski and his family lived. In August 1936, after his wife Helene and daughter Regina arrived in New York, the family moved a street across to 89 Eastchester Road, then later to 94 Hillside Avenue, also in New Rochelle.

The commute from New Rochelle to the Black Star office could be done by train, arriving at Grand Central Station, from which there was direct access to 420 Lexington Avenue, where the agency was located. In 1937 Kurt Kornfeld and Kurt Safranski met Ernest Mayer’s mother Mathilde Mayer in London and she travelled to New York with Kornfeld and stayed with her son and his family in New Rochelle from March to May, 1937. Finally, on 2 October, 1937, at the age of 68, she emigrated to New York to begin a new life with a new language.

At Black Star, Ernest Mayer worked with émigré photographers from Europe, including Ruth Bernhard, Ralph Crane (Rudolf Crohn), Andreas Feininger, Fritz Goro (Gorodiski), Carola Gregor (Gorodiski, née Margarete Meyer), Philippe Halsman, Fritz Henle, Lilly Joss (née Joseph), Lisa Larsen (née Rothschild), Walter Sanders (née Süssmann), Fred Stein, Roman Vishniac and Werner Wolff.