Cornet was born in St Kanzian in Carinthia in 1793, the youngest of eleven children; his father was a forester and mine manager.
As a child he received music lessons at Wilten Abbey [de] near Innsbruck, and he was noted for his beautiful voice.
In 1816 he took part in a gala performance of the oratorio The Liberation of Jerusalem by Maximilian Stadler, in which he replaced the indisposed intended tenor soloist.
He was in Paris in 1829, where he studied the part of Masaniello in Daniel Auber's opera La muette de Portici, and performed the role to critical success.
[1][2] Joseph Kürschner, his biographer in Allgemeine Deutsche Biographie, wrote: "With unreserved openness and straightforwardness as a director, energetic in his willingness, he was as excellent as a singer as he was as an actor.