Anton Haizinger heard Haizinger sing in concerts, and offered him an engagement at the theatre; Haizinger gave up teaching. Haizinger's first roles at Theater an der Wien, in 1821, were in two operas by Rossini, as Gianetto in "La gazza ladra" and Lindoro in "L'italiana in Algeri". He soon became well-known in Vienna. The role of Adolar in Weber's opera "Euryanthe", premiered in 1823 at the Theater am Kärntnertor, was created for him, and he was a soloist in the premiere in 1824 of Beethoven's Ninth Symphony at the same theatre. He continued studies with Antonio Salieri. At this time, Italian opera
La Scala a memorable concert conducted by Arturo Toscanini—twice La Scala's principal conductor and an associate of the composers Giuseppe Verdi and Giacomo Puccini—with a soprano solo by Renata Tebaldi, which created a sensation. La Scala hosted the first productions of many famous operas, and had a special relationship with Verdi. For several years, however, Verdi did not allow his work to be played here, as some of his music had been modified (he said "corrupted") by the orchestra. This dispute originated in a disagreement over the production of his "Giovanna d'Arco" in 1845; however the composer later conducted his "Requiem" there