Professor and Director of Institut für Kunstgeschichte at the University of Leipzig, 1958-1964. Jahn studied under August Schmarsow and beginning in 1919 was an assistant for Wilhelm Pinder. After World War II, Jahn was appointed the Director of the Fine Art Museum (Museum der bildenden Künste) in Leipzig. In 1958 he succeeded Heinz Ladendorf as Director of Institut für Kunstgeschichte at the University of Leipzig. He stepped down in 1964 and was succeeded by Ernst Ullmann. In 1973 he became emeritus. Jahn's Die Kunstwissenschaft der Gegenwert in Sebstdarstellung was one of the early attempts to address the methods of the discpline.
edited, Die Kunstwissenschaft der Gegenwert in Sebstdarstellung. Leipzig: 1924.
Dilly, Heinrich. Kunstgeschichte als Institution: Studien zur Geschichte einer Diziplin. Frankfurt am Main: Suhrkamp, 1979, p. 25; Metzler Kunsthistoriker Lexikon: zweihundert Porträts deutschsprachiger Autoren aus vier Jahrhunderten. Stuttgart: Metzler, 1999, pp. 187-90.