The libretto was written by Eugène Scribe, based on Paul Foucher's play Don Sébastien de Portugal which premiered at the Théâtre de la Porte-Saint-Martin on 9 November 1838[1] It is a historic-fiction about King Sebastian of Portugal (1554–1578) and his ill-fated 1578 expedition to Morocco.

[3] Mary Ann Smart has prepared a critical edition of the opera in French, which includes appendices with variants and additions that Donizetti made for a production in German at the Vienna Hofoper in 1845.

Sébastian's entourage includes the idealistic poet Camoëns and the Moor princess Zayda, whom he had rescued from being burnt at the stake for trying to escape the monastery she had resided in since her conversion to Christianity (O mon Dieu, sur la terre).

Fez, Morocco The reunion between Zayda and Ben-Selim is dampened by her refusal to marry the Moorish chief Abayaldos.

where he learns that Antonio has aligned himself with the Spanish Grand Inquisitor Dom Juan de Sylva and usurped the throne.

A court of law, Lisbon At Sébastian's trial, Zayda proves her love for him by testifying to his true identity and how he escaped death.