John Janssen, born of German-Belgian parents in the Dutch town of Weert, made his first experiences as a soloist as a boy soprano. Singing was part of the daily bread with the church choir of his father, who was a church musician. One and a half hour they practiced every day. Among the works performed was the eight-voices Missa Papae Marcelli by Giovanni Pierluigi da Palestrina. He discovered his passion for the piano at the age of nine and started teaching himself how to play the piano, purely by ear and without notes.
At eighteen he successfully passed the piano entrance exam at the Maastricht Conservatory. He completed his studies with the pianist Jo Dusseldorp with the A-act. His singing teacher Mya Besselinck, recommended Janssen to switch to his main subject, the opera singer Hans-Günther Grimm became his teacher. During his studies at the Conservatory, he worked as a piano teacher and choir conductor. Janssen completed his singing studies with the C-Act, after which he was allowed to study further for the Prix d'Exellence, which he received three years later. In 1977 he was engaged to the Musiktheater im Revier in Gelsenkirchen. Here he was able to build up a considerable repertoire. There he was promoted and shaped primarily by GMD Uwe Mund and directors such as Marcel Bluwal, Dietrich Hilsdorf, Christian Pöppelreiter, Thomas Rübenacker and above all Göran Järvefelt (a student of Ingmar Bergmann). John Janssen had his first guest engagement in 1978 at the Hamburg State Opera in the role of Harlequin in Ariadne auf Naxos by Richard Strauss, alongside Edita Gruberova as Zerbinetta and René Kollo as Bacchus.
In 1981 he saved a performance of "La Bohème" in Gelsenkirchen when he stepped in as Rodolfo for a colleague who was ill, which earned him great enthusiasm from the press and the public alike. His wide range of voices later resulted in engagements as a tenor.
In 1982 Wolfgang Sawallisch engaged him to the National Theater of the Bavarian State Opera in Munich, where he made his debut as Conte Almaviva in Le Nozze di Figaro alongside Margaret Price as Contessa, Lucia Popp as Susanna and Hermann Prey as Figaro under Wolfgang Sawallisch's direction in the direction of Günther Rennert. This was followed by the title role in Il Barbiere di Siviglia, directed by Ruth Berghaus, for which he received the so-called Star of the Week from the Munich evening newspaper.
In the Munich Opera Festival in 1983 he sang the role of Adriano in Wagner's Rienzi. Adriano is a so called Trouser role, written for a dramatic soprano, which was cast by Wolfgang Sawallisch with a high baritone, as a contrast to the tenor role Rienzi, sung here by René Kollo. For his interpretation of Adriano he received the Festival Prize of the Bavarian State Opera and was voted Singer of the Year 1984.
John Janssen sang under world-famous conductors such as Wolfgang Sawallisch, Carlos Kleiber, Hans Zöbeley, Julius Rudel, Carlo Franci, Laurent Wagner, Miguel Gomez-Martinez, Ferdinand Leitner, Georges Prêtre, Will Humburg, Armin Jordan, Uwe Mund, Donald Runnicles, Bernhard Klee and many others.
He sang the title role in Mozart's Don Giovanni for the first time in Gelsenkirchen, then at the National Theater of the Bavarian State Opera, at the Berlin State Opera Unter den Linden, at the Drottningholmer Slottsfestspiele in Stockholm, at the Hessian State Theater in Wiesbaden, at the opera house in Sankt Gallen and Bern, Switzerland. In Bern he stepped in for Ruggiero Raimondi in a gala performance with Gundula Janowitsch. Most recently (2009) he sang Don Giovanni at the theaters of Solingen and Remscheid, in a production of the Musikhochschule Köln directed by Professor Igor Folwill. Conductor was Professor Stefan Wehr.
The Gelsenkirchen staging of the opera Jakob Lenz by Wolfgang Rihm, directed by Thomas Rübenacker, in which John Janssen played the title role, had great success both at home and abroad and was invited to the Biennale in Zagreb, Paris, Rennes, Bonn, Munich, Frankfurt, Amsterdam and on a tour through South America to Rio de Janeiro, Belo Horizonte, Buenos Aires, Salvador Bahia and Sao Paolo. Janssen later sang Jakob Lenz in a new production at the Vienna State Opera, in Alessandria and at the Festivale Settembre Musica in Turin.
In addition to his work as an opera singer, Janssen sang recitals and concerts in the following cities: Gasteig and Herculessaal Munich, Schumannhaus Bonn, Basilique Véselay, Basilique Autun, Teatro La Fenice Venezia, Weber State University Ogden Utah (USA), Collegio Borromeo Pavía, Parma Lirica Parma , Pallazzo Ducale Colorno, Cremona Cathedral, Schouwburg Heerlen and many others.
John Janssen sang at the following opera houses: National Theater of the Bavarian State Opera Munich, Hamburg State Opera, Berlin State Opera Unter den Linden, Vienna State Opera, Hessian State Theater Wiesbaden, Theater der Stadt Basel, Oper Bern, Theater Sankt Gallen, Teatro Municipal Rio de Janeiro, Teatro La Fenice Venezia, Drottningholms Slottsteater Stockholm, Det Kongelige Teater Copenhagen, Teatro Massimo Bellini Catania, La Zarzuela Madrid, Teatro Verdi Mantova, Teatro Verdi Sassari, Canadian Opera Company Toronto.