He remained there until he was named Professor of Classical Philology Emeritus in 1951, except for the years 1942–1945, when he was at the University of Leipzig.
He is perhaps best known for his researches on Posidonius, but he also wrote highly original monographs on the Presocratics, Aeschylus, and Sophocles.
Although he was mainly a disciple of Wilamowitz, for a time in his youth he came under the influence of Nietzsche and the poetic circle of Stefan George.
His many writings in turn had a profound effect on the thought of Ernst Cassirer, Martin Heidegger and Wolfgang Schadewaldt.
In 1952 Reinhardt was inducted into the Order Pour le mérite für Wissenschaften und Künste and in 1956 was awarded an honorary doctorate from the University of Frankfurt.