Rosenmeyer was born on April 3, 1920, in Hamburg and attended the Gelehrtenschule des Johanneums from 1930 to 1938. He left Germany for England in 1939, and was interned for being a German citizen and transferred to Canada, where Martin Ostwald and Emil Fackenheim were in the same camp.
Rosenmeyer's early life began on April 3, 1920, in Hamburg, where he studied at the Johanneum School of Studies from 1930 to 1938. His departure for England in 1939 led to his internment as a German citizen before being relocated to Canada, where he shared a camp with prominent academics Martin Ostwald and Emil Fackenheim.