On the island of Cyprus, Venetian officers and the Cypriot populace are awaiting the arrival of the Moor Otello, the governor from Venice, whose ship is battling a violent storm. The storm subsides and Otello lands, to the joy of the crowd. Only Iago and Roderigo do not share the general happiness. Iago is bitter because Otello has named Cassio his lieutenant, instead of Iago; and Roderigo is unhappy because he is in love with Desdemona, Otello's wife. Iago is already plotting his revenge, and when Cassio appears, Iago and Roderigo make him drunk, then provoke a duel with Montano. Otello, summoned by the brawling, dismisses Cassio from his service. Desdemona arrives, and when all have gone, she and Otello again declare their love.
Iago, now Otello's confidant, continues his plotting. He advises Cassio to ask Desdemona to intercede with Otello for the disgraced officer's pardon. The Moor sees Cassio with his wife, and Iago plants the seed of jealousy, which grows as Desdemona pleads with her husband to forgive their old friend Cassio. Iago takes a handkerchief of Desdemona's from his wife, Emilia, who is Desdemona's companion. Later he will use it as evidence. When he and Otello are alone, he tells how he heard Cassio talk in his sleep about Desdemona, as if the two of them were lovers. Otello vows vengeance, and Iago swears to assist him and to furnish him with proof.
Ambassadors are coming from Venice. Before they arrive, Desdemona again broaches the subject of Cassio, and Otello openly accuses her of adultery. Later he spies on a meeting between Iago and Cassio, who displays a handkerchief he has mysteriously found in his room. It is Desdemona's, placed there by Iago. Otello cannot hear the two men's words, but the sight of the handkerchief convinces him. When he receives the ambassadors, he cannot restrain his jealous fury and, in front of all, insults his wife and hurls her to the floor. Iago feels that his triumph is near.
Desdemona is preparing for bed. As Emilia assists her, she sings a sad song about unhappy love. Emilia leaves; Desdemona prays and then goes to bed. Otello enters and warns her that he has come to kill her and demands her to atone for all her sins. Again she protests her innocence, but he refuses to believe her and strangles her. Emilia knocks, then bursts in to tell Otello that Roderigo, who, according to Iago's plot, was to kill Cassio, has been killed. Cassio lives. Desdemona moans, Emilia cries out in horror, and others come in, including Iago, whose villainy is revealed. Iago flees, pursued by the others, and Otello kills himself over Desdemona's lifeless body.