Act I. It is 1457. In the Hall of the Palazzo Ducale in Venice the Council of Ten and the members of the government are meeting together for an important decision. Loredano, member of the Council, and his friend Barbarigo arrive. The two learn that the Doge, apparently calm and serene, has preceded them into the chambers: before entering, all must sing the praises of Venetian justice. Conducted out of prison, Jacopo Foscari, son of the Doge, waits to be summoned before the Council: he salutes his beloved Venice that he has not seen for so long because exiled and banished from the city. An official tells him to hope for an act of clemency, but Jacopo rails against the atrocious hate he is the victim of. Lucrezia Contarini, wife of Jacopo, pleads his case before the Doge, who after all is his father, but, the Doge answers, she may ask and hope for justice only from heaven. As Pisana, a friend of Lucrezia's, announces that Jacopo has once more been condemned to exile, Lucrezia gives vent to her fury.
The senators comment the sentence while leaving the chambers: Jacopo has not confessed, but the letter he sent to the duke Sforza in Milan proves his guilt: Thus it is right that he should have to return to exile in Crete. The impartiality of Venetian justice must be clear to all, when even the Doge's son is condemned.
Only the Doge reflects bitterly on his destiny as prince, with his power much reduced by the Council of Ten, and as father, having to see his son languish without being able to help him. Lucrezia enters and pleads with her father-in-law to annul Jacopo's sentence, but the Doge tells her he cannot do this under Venetian law. Seeing the old man in tears for the destiny of his son, Lucrezia begins to hope.
Act II. Languishing in a dark cell, Jacopo in a moment of delirium sees the ghost of Carmagnola, the famous commander executed in Venice, advance toward him holding his severed head. Terrified, he faints, and comes to in the arms of Lucrezia, who has come to give him the sentence: not a sentence of death, but of exile, that will oblige them to forever live apart. But from afar is heard a barcarole that gives them hope. The Doge arrives and the three embrace, deeply moved. It is paternal affection and no longer authoritarian rigour that Jacopo now sees in his father, and this will be a comfort to him during his long exile. Accompanied by guards, Loredano arrives and tells him coldly that the Council has already decided: he must leave at once and forever for Crete. The three embrace once again, but Loredano separates them without pity causing the anger of Jacopo and Lucrezia; the Doge counsels calm. Jacopo is taken away by the guards. The counsellors and governors are in reunion to confirm the sentence. The Doge enters to preside. Then Jacopo is admitted, asking justice of his father since he is innocent, but he can do no more than advise his son to resign himself. Lucrezia arrives with Pisana and other ladies, holding their two children by the hand. Jacopo runs to embrace them and makes them kneel before the Doge, pleading for mercy. Barbarigo is touched by this scene and tries to soften the resolve of implacable Loredano. But this last and the senators are unshakeable. Jacopo must return to Crete and must leave alone, without his family. With this future before him Jacopo senses that death cannot be far away.
Act III. The square of St. Mark's fills with people in costume. A regatta is about to take place. Loredano and Barbarigo arrive and observe the happy crowd totally indifferent to the destiny of Foscari and the Doge. Loredano gives the signal for the race to begin, but suddenly trumpets blare and the people, frightened, move away. A galley is coming into port to take Jacopo to Crete. Before embarking he sadly bids farewell to Lucrezia and his children and tells his wife not to give his enemies the satisfaction of seeing her tears. But Loredano once more separates them to hurry up the departure. As Jacopo boards the galley Lucrezia faints.
In his private rooms, the Doge bemoans his tragic destiny: three of his sons have died early deaths and a fourth must endure bitter exile. Suddenly Barbarigo enters with a letter written by one Erizzo, confessing to the crime of which Jacopo was accused. The Doge thanks the heavens, but his joy is short-lived: Lucrezia enters in tears to announce the death of Jacopo, at the very moment the boat left. She goes out, invoking heaven's ire against her husband's persecutors. Then the members of the Council headed by Loredano are brought before the Doge: they have come to ask for his resignation, given his advanced age and his state of shock because of his son's death. For the Doge it is the final straw: twice in the past he had asked to abdicate and twice his request had been denied. He took an oath to remain in his functions until death, and now he will honour his pledge. But the Council is inflexible: the old Doge hands over the ring and the crown of office. Lucrezia arrives to accompany him out of the palace as the bells of St. Mark's start to chime. Loredano comes to tell him that Malipiero is the new Doge. At this news the old man dies.
The 1840s was a decade of intense activity for Verdi, who was writing operas for the four most important Italian theatres of the epoch: the Scala in Milan, La Fenice in Venice, the San Carlo in Naples and the Argentina in Rome. I due Foscari was composed for the last of these, the libretto assigned to his most trusted collaborator, Francesco Maria Piave, of a Venetian subject from a work in English of the same name by George Byron.
Arriving in Rome in September 1844, Verdi worked hard to keep his deadlines, stimulated by the vibrant Roman atmosphere; by November, the new opera was already being performed. Many other theatres also staged I due Foscari: the San Benedetto and Fenice in Venice, the Comunale in Bologna, the San Carlo in Naples, and outside Italy the Italian Theatre in Paris and Covent Garden in London. The productions outside Italy were enriched by a new cabaletta composed by the Maestro expressly for the tenor Mario at the request of the nobleman and composer Giuseppe Poniatovski.