As a tempest rages in the harbor of Cyprus, citizens await the return of their governor, Otello, a Moorish general in the Venetian army. When his ship is sighted, the Cypriots call on heaven to spare it.

Safely in port, Otello proclaims victory over the Turks ("Esultate!") Otello then enters his castle. His ensign, Iago, angered because a rival,Cassio, has been promoted to captain, plots his own advancement by fanning the secret desires of Roderigo, a Venetian dandy, for Otello's wife, Desdemona.

Meanwhile, the Cypriots gather around a bonfire. Iago, leading a drinking song (brindisi: "Inaffia l'ugola,") forces the easily intoxicated Cassio to drink a toast to Otello and his bride; the ensign next provokes Roderigo to duel with the reeling Cassio.

Otello, awakened by the brawl, storms out to demand an explanation; Iago pretends ignorance. As Desdemona joins her husband, he demotes Cassio, instructing Iago to restore order. Otello and Desdemona, left alone, tenderly recall their courtship ("Gi� nella notte densa ") and kiss three times before re-entering the castle.

By the castle garden, Iago advises Cassio to seek Desdemona's aid in regaining Otello's favor. Cassio goes off, leaving Iago to describe his view of his creator, a cruel demon who gives him ideas for evil machinations ("Credo.")

On Otello's arrival, the ensign makes innuendos about Desdemona's fidelity as they see her in the garden with Emilia (Iago's wife) and Cassio; yet he warns the Moor to beware of jealousy. Women, children and sailors bring flowers to Desdemona, whose beauty softens Otello's suspicions, but when she approaches him about Cassio's reinstatement, he grows irritable. Fearing he is ill, she tries to soothe his brow with a handkerchief, which he throws to the ground. Desdemona, confused, pleads her devotion, while Iago furtively wrenches the handkerchief from Emilia, who has retrieved it.

When the women leave, Otello accuses his ensign of destroying his peace of mind. Iago answers the Moor's demand for proof by pretending he has heard Cassio murmur Desdemona's name in his sleep ("Era la notte"); worse he says he saw in Cassio's hand the strawberry-embroidered handkerchief Otello gave her when he first courted her. Seconded by Iago, Otello vows vengeance ("Si, pel ciel.")

In the armory, Iago tells Otello that more proof is forthcoming and then departs as Desdemona greets her husband ("Dio ti giocondi.") The Moor hints at his suspicions but she fails to understand. When he demands the handkerchief he once gave her, she again pleads for Cassio, driving Otello to call her a courtesan. Tearfully, Desdemona swears her innocence; the Moor sends her away.

Spent with rage, Otello wishes heaven had taxed him with any affliction but this (" Dio! mi potevi scagliar,") then hides at the approach of Cassio and Iago. The ensign, flashing the handkerchief, manipulates Cassio's banter about his mistress, Bianca, so that Otello thinks they are joking about Desdemona. Cassio leaves as trumpets announce dignitaries from Venice. Otello swears to kill his wife.

In the great hall, the court enters to welcome Lodovico, the ambassador, who presents papers recalling Otello to Venice and naming Cassio governor. Otello loses self-control and hurls Desdemona to the floor. She begs forgiveness for her supposed crime. The courtiers try to console her, but Otello orders them out. As the Moor falls unconscious in a fit, Iago ironically salutes him as the "Lion of Venice." Act IV

In her room, as Emilia helps her prepare for bed, Desdemona sings a song about a maid, Barbara, who was forsaken by her lover (willow song: "Salce! Salce!") Startled by the wind she bids her companion goodnight, says her prayers ("Ave Maria ") and retires. Otello steals in and tenderly kisses Desdemona. When she awakens, he tells her to prepare for death; though she protests her innocence, he strangles her.

Emilia knocks with news that Cassio has slain Roderigo. Hearing Desdemona's death moan, she cries for help, bringing Iago, Lodovico and Cassio. When Emilia tells of Iago's treachery, he stabs his wife and rushes from the room.