He studied the ancient history of the Middle East, classical archaeology and Assyriology from 1954 to 1961 at universities in Munich, Berlin, and Ankara.
He received his doctoral degree in 1961 at the Free University of Berlin (thesis title: Keramik der Frühen Bronzezeit aus Inneranatolien).
From 1966 to 1969, he received a scholarship from the German Research Foundation (DFG) to support his habilitation, which took place in 1969 at Saarland University with his publication of Untersuchungen zur späthethitischen Kunst (Investigations of Late Hittite Art).
From 1994 to 2000, Orthmann was a professor and dean for art, classical and ancient studies at Martin Luther University of Halle-Wittenberg.
[1] Travels in near eastern countries and excavation campaigns in Ilica (Turkey) and in Mumbaqat (Syria) since 1973-1974 supported his work as a specialist in archaeology, particularly in the area of Hittite culture.