Stefan studied Biochemistry at the University of Tuebingen/Germany from 1981 to 1986. He completed his Masters in 1987 and moved to the Research Center in Juelich where he worked on amino acid producing bacteria during his PhD. He was awarded his PhD in 1991 and moved to the University of Illinois in Chicago as a research fellow of the German Science Foundation. In 1993 he was appointed as Junior Lecturer at the University of Tuebingen in the Institute of Physiological Chemistry. In 1998 Stefan was promoted to Senior Lecturer and moved to the Institute of Physiology at the University of Tuebingen. In 2000 Stefan moved to ANU as a Senior Lecturer in the School of Biochemistry and Molecular Biology. He was promoted to Associate Professor in 2006 and to full Professor in 2008. Stefan was treasurer and council member of the Australian Physiological Society from 2005-2009.