In 1885 he succeeded Theodor Mommsen (1817-1903) as professor of ancient history at the University of Berlin, where he remained until his retirement in 1917.
At Vienna he organized the Archaeologic-Epigraphic Seminary with archaeologist Alexander Conze (1831-1914).
Hirschfeld edited several volumes of the Corpus Inscriptionum Latinarum, in which he largely dealt with inscriptions of Gaul and Germania.
Other writings include: Untersuchungen auf dem Gebiete der römischen Verwaltungsgeschichte (1876), Inscriptiones Galliae Narbonensis Latinae CIL Vol XII (1888) and Inscriptiones Aquitaniae et Lugdunensis (1899).
In occasion of leaving the University of Vienna in 1885 he received a medal initiated by friends and students.