He performed internationally at leading opera houses and festivals, such as the Teatro Colón of Buenos Aires and the Zoppoter Festspiele.
He appeared in the world premieres of Wolf-Ferrari's I gioielli della Madonna in Berlin, Busoni's Die Brautwahl in Hamburg, and Lehár's Giuditta in Vienna.
He appeared as Escamilio in Bizet's Carmen, and in operas by Alban Berg, Julius Bittner, Marco Frank, Wilhelm Kienzl, Erich Wolfgang Korngold, Otto Nicolai, Hans Pfitzner, Ermanno Wolf-Ferrari and Alexander von Zemlinsky.
[5] He performed as a guest at the Liceu of Barcelona in 1927, at La Monnaie in Brussels in 1936, the Teatro Colón of Buenos Aires in the 1930s, and in London as Beckmesser in 1938.
[3] Wiedemann's roles included:[2] Beethoven: Berg: Bittner: Bizet: Donizetti: Humperdinck: Janáček: Kienzl: Korngold: Mascagni: Meyerbeer: Mozart: Mussorgski: Nicolai: Pfitzner: Puccini: Johann Strauss (son): Richard Strauss: Tchaikovsky: Verdi: Wagner: Despite the long duration of his career, there are only a few sound documents.
There are at least three recordings of individual scenes from the Vienna State Opera, as Alberich (with Luise Helletsgruber, Enid Szánthó and Dora With as Rheintöchter), as Klingsor and Beckmesser.