In accepting a commission from the Teatro La Fenice, Venice, in 1843, Verdi was breaking faith with La Scala, for which he had composed all his previous operas, and for which he had been approached to provide another for the following season. It proved a decisive departure: leaving aside Giovanna d’Arco (1845), arguably no more than a nostalgic gesture, and a revised version of La forza del destino (1869), the composer's grand homecoming to Milan would occur only after he felt secure enough to impose his own rules, with the revised Simon Boccanegra (1881), Otello (1887), and Falstaff (1893). Moving to Venice meant more than adjusting to a smaller stage; it called for a kind of personal drama for which there had been no space in works such as Nabucco or I lombardi. This in turn deprived Verdi of the rich fund of reference associated with that specific theatrical milieu, forcing him to take on the personality, as it were, of a quite different establishment. Indeed, the imprint of La Fenice can be felt at all stages of the genesis of Ernani, from censorship of the libretto to the distinctive vocal style of the score.

The success of Ernani at its premiere on March 9, 1844 – in spite of the sets not being ready, and the tenor having lost his voice and the soprano her sense of pitch – seemed testimony that the opera would stand on its intrinsic qualities. Confirmation came with its warm reception at many other opera houses, and Ernani greatly enhanced Verdi's reputation at the national and international level, establishing it as second only to Donizetti's among Italian opera composers. Verdi’s own theatrical instincts can plausibly take most of the credit: if the idea of the subject first came to Count Alvise Francesco (Nani) Mocenigo, director of La Fenice in 1843–44, it was Verdi who, exercising the right to choose his own libretto for the first time, rejected a series of suggestions (including Catherine Howard, Cola di Rienzi, I due Foscari, The Bride of Abydos, King Lear, Cromwello, and Allan Cameron) and became enthused only when Victor Hugo’s Hernani was mentioned.