Courtauld Institute professor and librarian, instrumental force in moving Warburg library to London and administering it duirng Warburg's mental illness. Saxl was born to Ignaz Saxl and Wilhelmine Falk (Saxl). His father was a distinguished state attorney in Vienna. Although of devout Jewish grandparentage, Saxl's father had rejected religion and the children were raised in a secular, culturally-Jewish home. After receiving an Abitur from the Maximilians gymnasium in 1908, where his classmate was the future art historian Emil Kaufmann, Saxl studied art history and archaeology in Vienna at the Institut für Österreichische Geschichtsforschung under the [second] "Vienna School" art historians Franz Wickhoff, Julius Alwin von Schlosser and Max Dvořák and in Berlin, 1909-1910 under Heinrich Wölfflin. Saxl completed his dissertation still only age 22, under Dvořák on various aspects of Rembrandt in 1912. The year before he had met the private scholar-art historian Aby M. Warburg. Saxl spent the academic year 1912-1913 on a stipend in Rome where he studied medieval texts on astrology and mythology. In 1913 he married Elise Bienenfeld and joined the Warburg Library in Hamburg as the librarian. Saxl fell under Warburg's spell, adopting his mentor's methodology, viewing the history of art as the transmission of pagan myth through literature and art of the medieval and renaissance periods. Although Saxl had specialized in the baroque era in Vienna, his interest in the medieval period and astrological manuscripts, alive before he met Warburg, took on new meaning. The first volume of a catalog of astrological manuscripts appeared in 1915. When World War I erupted, Saxl served as a first lieutenant in the Austro-Hungarian army (1914-1918) seeing action in Italy and 1918-19 as a teacher for the army. In 1919 he returned to the Warburg. Warburg himself was indefinitely committed to a mental asylum and Saxl took over the day-to-day running of the library foundation, and developing it, with colleague Gertrud Bing, from 1922 onward, according to Warburg's wishes into the Warburg Institut, aligning it with the newly founded University of Hamburg in 1921. Saxl enlisted Warburg's brothers, financiers in New York and Hamburg, to assist financially. Saxl initiated the Vorträge der Bibliothek Warburg, publishing an article himself in the series. Saxl was a privatdozent (1922-1923) and then lecturer between 1923-1933 for the University in Hamburg. In 1923 Saxl and another Warburg exponent, Erwin Panofsky, jointly authored an important study building on Warburg's principle of pictorial themes migrating to intellectual realm, using Dürer's Melancholia I. Warburg returned from hospitalization in 1924. Saxl traveled on research outings to Rome, London, Vienna and Heidelberg. A second volume of the astrological manuscripts appeared in 1927. At Warburg's death in 1929, Saxl succeeded him as director. Saxl foresaw the disasters the Nazis promised for scholarship in Germany, especially for those institutions intimately connected with Jewish founders and scholars such as Saxl and Warburg. He gave fellow Schlosser student Otto Kurz a position as librarian when Kurz could find no work in anti-semitic Austria. Saxl himself hoped to move the Warburg to Holland, but when those deliberations failed, Saxl contracted with Samuel Courtauld (1876-1947, principal benefactor of the Courtauld Institute) and Arthur Hamilton Lee (Viscount Lee of Fareham, 1868-1947, Chairman, Management Committee of the Courtauld Institute of Art) to move the Warburg Library "on loan" to the Courtauld Institute at the University of London in 1933. At the same time, other Hamburg scholars who were connected with the Warburg followed. These included the recently graduated Hugo Buchthal, Edgar Wind and E. H. Gombrich. The library was temporary housed in the basement of Thames House. In 1938 the Warburg lost this temporary housing and the papers had once again to be crated up. Funds to maintain this unusual think-tank were particularly hard to come by. Saxl devoted the remaining years of his life to maintaining the Institute, at the cost of his own scholarship. When Britain entered the World War II, the Warburg was evacuated to Denham, England, and Saxl hired Buchthal to be its librarian for most of the 1940s and as a scholar to keep it responsive to the needs of research. Saxl became a British citizen in 1940. In 1944 the Warburg Institute was officially made part of the University of London. Between 1945 and 1946, he traveled to the United States, securing cooperation on a number of scholarly projects, among them the Illustrated Bartsch, (the Peintre graveur of Adam von Bartsch, updated scholarship and illustrations), and a Census of Classical Works of Art Known to the Renaissance, sparked by the enthusiasm of Karl Leo Heinrich Lehmann, Richard Krautheimer and Panofsky. Saxl spent the final years of his life maintaining the Warburg. It was often noted by biographers that he sacrificed personal scholarship in order to run the Warburg. At his death in 1948, he was succeeded by Henri Frankfort. The remaining volumes of the Verzeichnis astrologischer und mythologischer illustrierter Handschriften, renamed the Catalogue of Astrological and Mythological Illuminated Manuscripts of the Latin Middle Ages, were issued in 1953 by Hans Meier and Harry Bober. Bing was his life partner and the two maintained a house in Dulwich, England, where they entertained.
Saxl represents in some ways the "purest" continuation of Aby M. Warburg's methodology. Other Warburg scholars (Wind, Gombrich, Panofsky) developed their own stamp. But Saxl remained fascinated by the transmission of mythology through the language of forms on which Warburg had founded his institution. His methodological influence was particularly profound on Jean Adhémar.