In 1968, Gruberová made her operatic debut in Bratislava as Rosina in Rossini's "Il barbiere di Siviglia". After winning a singing competition in Toulouse, she was then engaged as a soloist of the opera ensemble of the J. G. Tajovský Theatre in Banská Bystrica, Slovakia, from 1968 to 1970. Since communist Czechoslovakia was going through normalisation, during which the borders were closed with non-communist countries, Medvecká surreptitiously arranged for an audition for Gruberová in the summer of 1969 at the Vienna State Opera, which immediately engaged her. The following year, she made her breakthrough when she sang the Queen of the Night in Mozart's "Die Zauberflöte". Gruberová then decided to emigrate to the West. In subsequent years, she became a soloist in Vienna and was invited to sing at many of the most important opera houses in the world, especially in coloratura roles.