Born in Geldern, Germany, Guido Jentjens studied at the Musikhochschule Köln and began his singing career at the Opera Studio of the Deutsche Oper am Rhein in Düsseldorf.
From 2005 to 2013 Guido Jentjens was an ensemble member of the Staatstheater Nürnberg.
Other permanent and guest engagements have taken him to Augsburg, Erfurt, Karlsruhe and Wiesbaden, as well as to the opera houses in Bielefeld. Krefeld/Mönchengladbach, Kassel, Halle, Würzburg, Dortmund, Essen and others.

Last season, he appeared as Boris Godunov in Mussorgsky's work of the same name at the New National Theatre Tokyo (musical director Kazushi Ono, stage director Mariusz Trelinski).
In recent seasons he has also celebrated highly acclaimed role debuts as Duke Bluebeard in Bela Bartók's Duke Bluebeard's Castle and as Hagen in Wagner's Götterdämmerung.

Guido Jentjens' repertoire includes all great Wagnerian bass and bass-baritone roles such as König Heinrich (Lohengrin), Hans Sachs and Pogner (Die Meistersinger von Nürnberg), Landgraf Hermann (Tannhäuser), Hunding (Walküre), Daland (Der fliegende Holländer), Gurnemanz (Parsifal) and König Marke (Tristan und Isolde), Hagen (Götterdämmerung) and Wotan (Rheingold). His wide repertoire also features roles like Baron Ochs auf Lerchenau (R. Strauss, Rosenkavalier), Orest (R. Strauss, Elektra), Osmin (Mozart, Entführung aus dem Serail), Sarastro (Mozart, Zauberflöte), Rocco (Beethoven, Fidelio), Philipp (Verdi, Don Carlo), Mephisto (Gounod, Faust), belcanto roles such as Silva (Verdi, Ernani), Banquo (Verdi, Macbeth), Des Grieux (Massenet, Manon) as well as numerous roles from Handel operas.

In the past seasons he celebrated highly acclaimed role debuts as Blaubart in Bela Bartók's Herzog Blaubarts Burg and as Hagen in Wagner's Götterdämmerung.

Guest appearances in opera and concert have taken Guido Jentjens among others in Berlin to the Staatsoper Unter den Linden, Deutsche Oper and Komische Oper, to the Staatsoper Hamburg (world premiere of Zemlinsky, König Kandaules under Gerd Albrecht), to the Semperoper Dresden (Matthus, Farinelli), to the Theater am Gärtnerplatz and the Prinzregententheater in Munich, the Philharmonie Köln and the Gewandhaus Leipzig.