 From 1957 until 1962, Mittelberger was an assistant at the Institute of Indology in Vienna.In 1963, he became a scientific clerk for Indo-European linguistics and the Hittite language at the "Institut voor Osterse Talen" at the University of Utrecht.From 1964 until 1971, he was assistant at the Institute of Linguistics at the University of Würzburg, where in 1969, he passed his habilitation for Comparative (Indo-European) linguistics.