Johannsen's Evangelist début with Bach's Christmas Oratorio was in December 1998 and his first recital was Schubert's Die schöne Müllerin.
Johannsen has worked with conductors such as Nikolaus Harnoncourt, René Clemencic, Georges Prêtre, Sir Neville Marriner, Peter Schreier, Dennis Russell Davies, Thomas Hengelbrock, Jordi Savall, Roy Goodman, Enoch zu Guttenberg, Jos van Veldhoven and Rudolf Lutz.
Johannsen made his debut as "Die Allegorie der Bewegungen" in Wolfgang Sauseng's church opera Das Staunen des Ezechiel (Vienna 2002).
In the 2005/2006 season, Johannsen was a member of the ensemble of the Luzerner Theater [de]'s (Il barbiere di Siviglia, A Night in Venice).
During the 2010 Carinthian Summer [de], Johannsen was cast for the world premiere of Die Geburt des Täufers by Jyrki Linjama.