He made his debut in 1896 in Brno (Brünn) and proceeded to sing leading roles in Bohemia and Germany, appearing at Breslau and, in 1898–99, at Berlin.
[5] Slezak's international career commenced in London at the Royal Opera House, Covent Garden, where he sang Siegfried (a punishing role that he would soon drop from his repertoire) and Lohengrin in 1900.
[6] A tall, barrel-chested man, Slezak possessed a large and attractive lyric-dramatic voice which enabled him to undertake all but the very heaviest Wagnerian parts such as Tristan or Siegfried.
They were produced by several different record companies and include arias, duets and songs by a wide selection of composers, ranging from Mozart to Wagner.
[7] Slezak's autobiography, published in 1938 in English as Song of Motley: Being the Reminiscences of a Hungry Tenor,[8] contains pen-portraits of many of the musicians and artists with whom he worked, including Gustav Mahler, Arturo Toscanini and Cosima Wagner.
It describes his tours of America, Russia and the Balkans and recalls his doomed audition for Frau Wagner at Bayreuth, when he foolishly chose to sing music from Pagliacci.
[citation needed] Later in life, he published several very humorous, semi-autobiographical books, notably: In 1932, Slezak began appearing in German cinema.