He was the son of Wilhelm Feldman, a writer, playwright, literary critic and historian, and Maria Kleinman, a translator of Western literature. His family was of Polish Jewish ethnicity. He graduated from secondary school in Kraków in 1917, then studied law and history in the Jagiellonian University, among others under the direction of Władysław Konopczyński and Stanisław Kot. During 1918-1920 he served as a volunteer in the Polish Army. In 1922 he was appointed assistant in the Seminar of History of the Jagiellonian University, in 1923 he defended his doctor thesis Polska w dobie wielkiej wojny północnej 1704-1709" elaborated under the supervision of Stanisław Kot. In 1927 he passed examination for post-doctoral degree based on his study Polska a sprawa wschodnia 1709-1714 and became senior reader in the Department of Universal History of the Jagiellonian University. Since 1937 he was associate professor, and at the same time took over the management of the Department of Modern History of the Jagiellonian University and was the chief thereof until the outbreak of World War II and since the end of the war. He lectured the universal history and the diplomatic history of the 19th century and 20th century; since 1929 he additionally lectured the same subjects at the School of Political Sciences in Kraków. He was a visiting lecturer in Paris, was involved in the activities of the International Congress of Historical Sciences in Warsaw in 1933 as well as in Zurich in 1938, was one of the initiators of the International Institute of the History of the French Revolution in Paris. His friends included historians Władysław Konopczyński, Stanisław Kot, Marian Kukiel, Stanisław Kutrzeba as well as foreign scholars.
1939–1945
During World War II he was wanted by the Gestapo because of his pre-war scholarly researches of German-Polish relations, which criticized German policy towards Poland. Some time he worked as archivist in the Ossolineum in Lviv, then he went into hiding in the Franciscan monastery in Hanaczów near Lviv. Then he moved to Warsaw. He took part in the underground education. War experience accompanied by studies upon Christian philosophy made him a deeply believing catholic. During the Warsaw Uprising in 1944, unfit for military service because of his heart disease and myopia, he served in the ranks of the monastery in Kalwaria Zebrzydowska.
Most valued and republished part of his production includes researches on German-Polish relations and the times of Augustus II the Strong.
German-Polish relations
He paid much attention to the policy of Otto von Bismarck towards Poles; after a series of partial studies he published a monograph Bismarck a Polska , in which he gave a comprehensive and critical analysis of Bismarck's policy regarding Polish question; the monograph was also of political importance as it influenced public opinion by an exposure of historical sources and continuity of the anti-Polish policy of Germany. During World War II the book was prohibited and hunted down by German occupation authorities.
He was a pioneer of scholarly research of the history of Poland in time of the Great Northern War during the reign of Augustus II the Strong. He published a series of monographs: Polska w dobie wielkiej wojny północnej 1704-1709 continued in Polska a sprawa wschodnia 1709-1714 and Geneza Konfederacji Tarnogrodzkiej published in "Kwartalnik Historyczny", and a monograph of king Stanisław Leszczyński. Feldman was the author of the statement, that the period of the Wettin dynasty in Poland was featured not only by a decline of the country, but it was also the beginning of progressive thought and inner rebirth of the nation. The new tendency can be traced in the Tarnogór Confederation.
Other research
In his work Sprawa polska w roku 1848 he presented an outline of Prussian and Russian policy towards the situation on lands of partitioned Poland during the Revolutions of 1848. Józef Feldman researched the scholarly production of Michał Bobrzyński, Szymon Askenazy and Wacław Tokarz. He was an editor of the Cambridge History of Poland and prepared a new revised edition of his father's, Wilhelm Feldman, classical monograph Dzieje polskiej myśli politycznej 1864-1914 .
