Othello is set in Venice during an argument between rich man Roderigo and his friend Iago, who are trying to win Desdemona's hand in marriage. Roderigo is upset about Desdemona's marriage to Othello, a general whom Iago begrudgingly serves as ensign. 

Iago and Roderigo cry out to Brabantio that his daughter Desdemona has been stolen by and married to Othello, the Moor. Brabantio finds out that Desdemona is missing and gathers officers to find Othello.

At Othello's lodgings, Cassio arrives with an urgent message from the duke, requesting Othello's help in the matter of the Turkish invasion of Cyprus. Brabantio accuses Othello of stealing his daughter by witchcraft, but the duke and senate are sympathetic towards Othello. 

Othello explains that he wooed and won Desdemona not by witchcraft but with stories of his adventures in travel and war. The duke finds Othello's explanation convincing, and Desdemona defends her choice in marriage and announces her allegiance to her husband.

The duke orders Othello to go to Cyprus to aid in the defense against the Turks. Desdemona insists on accompanying her husband on his trip, and preparations are made for their departure. The following day, two gentlemen, Montano, the governor of Cyprus, and Cassio arrive in Cyprus. 

Othello's ship is sighted, and the group heads to the harbor. Cassio greets Desdemona by clasping her hand, and Iago tells the audience that he will use "as little a web as this" hand-holding to ensnare Cassio.

Othello arrives at a reveling party to celebrate Cyprus's safety from the Turks. Roderigo complains to Iago that he has no chance of breaking up Othello's marriage, but Iago assures him that Desdemona will lose interest in Othello and seek sexual satisfaction elsewhere. 

He counsels Roderigo to cast Cassio into disgrace by starting a fight with him at the evening's revels. In a soliloquy, Iago explains that eliminating Cassio is the first crucial step in his plan to ruin Othello.

Othello gets Cassio drunk and sends Roderigo to start a fight with him. Provoked by Roderigo, Cassio chases Roderigo across the stage. Governor Montano attempts to hold Cassio down, and Cassio stabs him. Iago sends Roderigo to raise an alarm in the town. 

The alarm is rung, and Othello arrives to still the commotion. When Othello demands to know who began the fight, Iago feigns reluctance to implicate his "friend" Cassio, but he ultimately tells the whole story. Othello strips Cassio of his rank of lieutenant.

Iago frames Cassio and Desdemona as lovers to make Othello jealous. In an attempt at reconciliation, Cassio sends some musicians to play beneath Othello’s window. Iago then tells Cassio that he will frame Cassio and Desdemona as lovers to make Othello jealous. 

As Cassio is about to leave, Othello and Iago return, feeling uneasy and confused. Desdemona comes to call Othello to supper and finds him feeling unwell. She offers him her handkerchief to wrap around his head, but he finds it too little and lets it drop to the floor. 

Desdemona and Othello go to dinner, and Emilia picks up the handkerchief, which he plants in Cassio’s room as evidence of his affair with Desdemona.

When Othello demands “ocular proof” that his wife is unfaithful, Iago says that he has seen Cassio “wipe his beard” with Desdemona’s handkerchief—the first gift Othello ever gave her. Othello vows to take vengeance on his wife and Cassio, and Iago vows to help him. 

When Othello sees Desdemona later that evening, he demands her handkerchief of her, but she tells him she does not have it with her and attempts to change the subject by continuing her suit on Cassio’s behalf. This drives Othello into further rage, and he storms out.

Cassio comes onstage, wondering about the handkerchief he has just found in his chamber. Iago instructs Othello to hide nearby and watch as Iago extracts from Cassio the story of his affair with Desdemona. 

While Othello stands out of earshot, Iago pumps Cassio for information about Bianca, causing Cassio to laugh and confirm Othello’s suspicions. Bianca herself enters with Desdemona’s handkerchief, reprimanding Cassio for making her copy out the embroidery of a love token given to him by another woman. 

When Desdemona enters with Lodovico and Lodovico gives Othello a letter from Venice calling him home and instating Cassio as his replacement, Othello goes over the edge, striking Desdemona and then storming out.

The next night, Othello accuses Desdemona of being a whore and ignores her protestations. Later that night, Othello ominously tells Desdemona to wait for him in bed and send Emilia away. Meanwhile, Iago assures Roderigo that everything is going as planned: to prevent Desdemona and Othello from leaving, Roderigo must kill Cassio. 

Iago enters shortly thereafter and flies into a pretend rage as he “discovers” Cassio’s assailant Roderigo, whom he murders. Cassio is taken to have his wound dressed.

As Othello stands over his sleeping wife in their bed-chamber, Desdemona wakes and attempts to plead with Othello, asserting her innocence, but Othello smothers her. Emilia enters with the news that Roderigo is dead, and Othello asks if Cassio is dead too. 

Desdemona changes her story before dying, claiming she committed suicide. Othello tells Emilia that he killed Desdemona for her infidelity, which Iago brought to his attention.

Montano, Gratiano, and Iago enter the room, and Iago tries to silence Emilia. Othello, initially believing Iago told the truth, becomes weeping and tries to kill him. Iago kills Emilia and flees, but Lodovico and Montano capture him. They bring Cassio, who is in a chair due to his wound. 

Othello wounds Iago and is disarmed. Lodovico tells Othello to return to Venice for trial. Othello makes a speech about his wishes and kills himself with a hidden sword. Lodovico gives Othello's house and goods to Gratiano and orders Iago's execution.