Bang Kaup did study Manchu, Old Persian, Avestan, and Mongol with Charles de Harlez.
In 1893 and 1909 he brought out a new edition of ancient Persian inscriptions together with Friedrich H. Weissbach and wrote several articles on the subject.
When the First World War broke out, Bang left Belgium and in 1917 became professor of Turkish Studies in Frankfurt.
In 1918 he was appointed professor at the University of Berlin where he continued the researches about the Turfan manuscripts, especially Manichaean and Christian texts.
Bang elaborated the classical issues in the historical grammar of the Turkic languages in his several writings (“Vom Köktürkischen zum Osmanischen,” “Monographien zur türkischen Sprachgeschichte”).