Despite successes - "the audience idolises me and the newspapers are full of the highest praise" - Janssen recognised he had no long-term future in Austria, and began reaching out to connections in the United States.
Narrowly escaping Austria in March 1938 ahead of the Anschluss, he temporarily settled in France, from where he visited South America to give some performances in Buenos Aires, before eventually emigrating to the United States.
Though he continued to sing his old roles, as well as occasional roles such as Don Fernando in Beethoven's Fidelio, Jochanaan in Strauss's Salome and The Speaker in Mozart's Die Zauberflöte, a shortage of suitable singers also pressured him into singing those heavier bass-baritone Wagner parts to which his voice was less well suited: for example Hans Sachs in Die Meistersinger von Nürnberg and Wotan/the Wanderer in Der Ring des Nibelungen.
In 1943 he succeeded Friedrich Schorr at the Met as the first heroic bass-baritone of the house; this meant the majority of Janssen's Metropolitan performances would now be of these heavy roles, to the greater detriment of his voice.
He also sang major baritone roles of Giuseppe Verdi, including Conte di Luna in Il trovatore as well as Renato in Un ballo in maschera and Iago in Otello.
There is a recording derived from the 1930 Bayreuth Festival with him performing Wolfram's music, while he sang the role of Don Pisarro in a 1944 radio broadcast of Beethoven's Fidelio with Arturo Toscanini conducting.
[24][25] Prieberg[citation needed] published the analysis of his private archives under the title Handbook 1933-1945 German musicians in the electronic self-publishing as a resource on a CD-ROM as a pdf file.