Afterwards, he worked as a lecturer at the universities of Besançon (from 1882) and Nancy (from 1884).
From 1887 to 1902 he was a professor of history at the University of Nancy.
From 1904 he served as a professor at the Sorbonne in Paris, then in 1919 relocated to the University of Strasbourg, where in 1927 he was named academic rector.