Il Giuramento was the first of Mercadante's so-called reform operas, and was the composer's first major success with the Italian public. Although he was much loved in his native land, his operas had enjoyed, up until Il Giuramento, less success than those of his colleagues Donizetti and Bellini. The premiere took place at the Teatro alla Scala of Milan on March 11, 1837. The reaction of the public and the critics was so positive that shouts of "viva il maestro" rang through the hall after the beautiful extended introduction. The critics wrote that this was Mercadante's masterpiece, and that although they had waited a long time for it, they had always believed in their beloved Mercadante. The ensemble pieces of Il Giuramento were particularly admired by other composers, especially Liszt. This work helped further the trends in Italian opera toward a more Romantic approach to operatic storytelling, and toward a greater involvement of the chorus and orchestra in the scenic tableaux. The harmonies are more adventuresome, and the orchestral palette isexpanded and used with greater intelligence. The music in general is more directly tied to the content of the drama.

Il Giuramento was composed after Mercadante's sojourn in Paris and his exposure to the French grand operas of Meyerbeer, Halévy, and others. It shows an appreciation for their experiments in musical dramaturgy, and employs the kinds of subject matter that infused French works of the time with a popular and social appeal. Mercadante had specific ideas about where the new trends in operatic composition should lead. He wrote to a friend that he wanted his new reform operas to have leaner, simpler vocal lines, and greater variety in the orchestrations, forms, and formulas of the music. The story was made into a libretto by Gaetano Rossi, and based on a work by the French author Victor Hugo. Angelo, Tyran de Padoue had been a huge success at the Théâtre-Français, and it is likely that Mercadante saw the play while he was living in Paris. Donizetti's Lucrezia Borgia had also been based on a Victor Hugo play, and its stunning success probably influenced Mercadante's choice of a source for his opera. The introduction and the first-act finale are both highlights of the work, and contain innovative writing and formal invention, but the third act contains Mercadante's finest music. The text of this act is quite faithful to the Victor Hugo play, and inspired the composer's best writing. Il Giuramento continues to be revived and appreciated by audiences in the twenty-first century.

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