After starting a commercial apprenticeship in the art trade, he studied German, history and education in Hamburg from 1971 to 1976.
After the Staatsexamen, he studied art history in Berlin and Hamburg from 1977 to 1985, graduating with a doctorate (Dr.
While still a student, he inventoried the daguerreotype collection at the Museum für Kunst und Gewerbe Hamburg.
In 2004, the Faculty of Philosophy of the Rheinische Friedrich-Wilhelms-Universität Bonn, where he had been teaching since 1989, awarded him the title of Honorary Professor.
Dewitz conceived a number of outstanding and highly regarded exhibitions, his first already during his studies at the Städtisches Museum Braunschweig on war photography, which he then also made the subject of his dissertation.