Since 1951, Neumann lectured in Germanic philology at the University of Göttingen. In 1955 he was appointed a guest professor at the Free University of Berlin. He was a visiting professor at Ohio State University in 1956. From 1959 to 1971, Neumann was Professor of German Philology, Old German Studies and Nordic Studies at the Free University of Berlin. During this time, he also served as Director of the Germanic Seminar (1957-1971) and Rector (1959-1961).
Neumann retired in 1971, and died in Berlin on 28 March 1985. He is buried at Waldfriedhof Dahlem.