During the 2010 Carinthian Summer, Johannsen was cast for the world premiere of Die Geburt des Täufers by Jyrki Linjama. In 2010, Johannsen was engaged as Tamino in Mozart's the Magic Flute at the Staatstheater am Gärtnerplatz in Munich. In the 2008/2009 season, he debuted at the Volksoper Wien in Eduard Künneke's operetta Der Vetter aus Dingsda and at the Ludwigsburger Schlossfestspiele in Mozart's Die Entführung aus dem Serail (Pedrillo, later also Belmonte). Here he worked with the directors Tatjana Gürbaca ( Zaide) and David Hermann ( Jewgenij Onjegin). In the 2005/2006 season, Johannsen was a member of the ensemble of the Luzerner Theater 's ( Il barbiere di Siviglia, A Night in Venice). On a tour of Japan in 2004, he appeared in Così fan tutte. In 2004, there were productions at the Wiener Kammeroper (a Monteverdi project with Lorenz Duftschmid and Philipp Harnoncourt) as well as at the Schlosstheater Schönbrunn (Janáček's The Cunning Little Vixen as a project of the opera class Parik/Nickler). Afterwards he was at the Lehár Festival Bad Ischl in 2003. Johannsen made his debut as "Die Allegorie der Bewegungen" in Wolfgang Sauseng's church opera Das Staunen des Ezechiel (Vienna 2002). 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, Johannsen's Evangelist début with Bach's Christmas Oratorio was in December 1998 and his first recital was Schubert's Die schöne Müllerin. He attended masterclasses with Dietrich Fischer-Dieskau, Christa Ludwig and Roger Vignoles. In 2005, he completed his studies - Lied and oratorio with Robert Holl, opera school with Ivan Parik and Reto Nickler. His voice teacher was Margit Fleischmann Klaushofer. Since 1998, he has been a member and soloist of the Arnold Schoenberg Choir and Concentus Vocalis Wien. He began studying church music in Oberschützen, which he continued at the University of Music and Performing Arts Vienna (organ with Alfred Mitterhofer, choir and ensemble conducting with Johannes Prinz and Johannes Hiemetsberger, composition with Wolfgang Sauseng) and passed the 1st diploma examination in 1999. Johannsen spent his upper school years at the Protestant Music High School. At the age of seven, he became a piano student at the Oberwart music school, then he changed to Martin Hopfmüller (full professor for Protestant Church Music at the University of Music and Performing Arts Graz). He grew up in Markt Allhau in Burgenland. Born in Vienna, Johannsen is the son of the protestant pastor Wolfgang and the professor of religion Ilse Johannsen.