German author of one of the monumental papal histories, Geschichte der Päpste seit dem Ausgang des Mittelalters, 16 vol. (1886–1933; History of the Popes from the Close of the Middle Ages).

While a student, Pastor became acquainted with the leading historians of his day. He became a lecturer at the University of Innsbruck (1881), where, in 1887, he was appointed professor of modern history. He later became director (1901) of the Austrian Historical Institute, Rome, and Austrian ambassador (1920) to the Vatican. He was knighted by Emperor Francis Joseph of Austria in 1908 and was created a baron in 1916.

Pastor's works include more than 12 monographs, the best-known being his Geschichte der Päpste. In 1881 Pastor caused Pope Leo XIII to open the Vatican archives, heretofore unavailable to scholars; Pastor also consulted archives throughout Europe. His papal history emphasized objective scholarship, treated dark periods of the papacy with frankness, and concentrated on individual popes rather than on the papacy as an institution. Another major work is his edition of Geschichte des deutschen Volkes, 8 vol. (1893–1926; “History of the German People”), by one of his former teachers, Johannes Janssen.