Oskar Rosenfeld was born to a Jewish family in Koryčany, Moravia (now Czech Republic). After completing his studies in 1908, he moved to Vienna, where he met Theodor Herzl and became active in Zionist organizations. He wrote for newspapers and journals about art, theater, and literature. In
1907, together with writers Hugo Zuckermann, Egon Brecher, and others, he co-founded a Jewish theater group to perform modern Jewish dramas in the German language. He worked for the group as a director and playwright as well as an actor. He also translated classical and modern Yiddish literature by Sholem Aleichem and others. His first novel, Die vierte Galerie, was published in 1910. He served in the Austro-Hungarian Army in World War I. He went to work for the illustrated weekly Die neue Welt, later becoming its editor-in-chief. The 1938 Anschluss (annexation) of Austria by Nazi Germany forced the end of Rosenfeld's career in Vienna. He and his wife Henriette took refuge in Prague, where he continued to work as a journalist. His wife went on to England in anticipation of his joining her, but the outbreak of World War II made this impossible. In 1941, Rosenfeld was deported to the Łódź Ghetto in Poland. He worked in the Ghetto archives, where he assisted with the publication of the community's newspaper. He was deported in 1944 to Auschwitz, where he was killed.
His diary, written in the Łódź Ghetto in a series of more than 20 notebooks, was hidden and survived the war. Eventually it was acquired by the Yad Vashem Library in Jerusalem. It was published in 2002 as In the Beginning Was the Ghetto.