Career
He is the former curator at the museum of Trelleborg and Middelaldercentret, where he worked from 1994–1999 and again from 2004–2015. Today he is a self employed historian. While working at Trelleborg he recreated the Viking game of knattleikr and injured his knee so badly that he had to use crutches for a time.
Johannessen has written several non-fiction books about both the middle ages and the viking age and historical novels.
Furthermore he has hosted a series of programs on the regional television Øst (sub-channel of television 2) about historical location Region Zealand an he has participated in historical quiz shows such as Historiequizzen (The History Quiz) on DR K. He also acted as historical expert in documentaries and series. He is very interested in World War I and has founded a reenactment group that portraits a group of German soldiers at the Western Front.
