In the opening scene, Iago is complaining to Roderigo about Othello, his Commander, passing him over to promote the Cassio to be his Lieutenant. He also revels that he thinks Othello slept with his wife. He does not know with certainty, but he vows to get revenge anyway. Iago first asks Roderigo cause a big scene to tell Desdemona's father, Brabantio, that his daughter has left to marry Othello. This is a marriage Brabantio opposes because Othello is black, and Desdemona did not get her father's permission. Brabantio confronts Othello, and they take their argument to the Duke, who has summoned Othello to ask him to sail to Cyprus to stop a Turkish invasion. The Duke gives Desdemona permission to travel with Othello, and basically tell Brabantio that Othello is a good man. By the time they reach Cyprus the foreign threat has gone.

Iago manipulates Roderigo into starting a fight with Cassio. Iago will get Cassio to drink to much; that is the only way Cassio would fall for such a thing as a street fight. Iago has his revenge on Cassio when Othello strips him of his rank for misbehavior. Then Iago decides to make Othello believe his wife has been unfaithful with Cassio. He encourages Cassio to ask Desdemona to plead with Othello to be reinstated. Iago tells Othello that Desdemona is Cassio's lover. Trusting Iago, and mad with jealousy, Othello promotes Iago and asks Iago to help him kill Cassio and Desdemona.

Iago plants Desdemona's handkerchief in Cassio's room. Cassio gives it to his mistress, Bianca. Othello believes Bianca's possession of the handkerchief is proof that Desdemona and Cassio are lovers. He verbally abuses his wife in front of others, who are shocked at the change in the noble and powerful man.

Iago then manipulates Roderigo into trying to kill Cassio. The attempt goes wrong, and Cassio wounds Roderigo. Seeing this from the shadows, Iago runs up and stabs Cassio in the leg. Othello hears Cassio cry out and thinks Iago has killed him. He returns home, ready to kill Desdemona. Meanwhile, Iago "finds" the wounded Cassio and accuses Bianca of hurting Cassio. Iago quietly kills Roderigo and sends Emilia to Desdemona with the news of what has happened.

Othello reaches the sleeping Desdemona with an elaborate soliloquy showing his pain and sadness over what he thinks he must do. He kisses her, wakes her, and accuses her again. Despite her protests that she loves him and is innocent, he smothers her. Emilia enters and Desdemona revives for a moment, as she dies, she says that Othello is innocent of her death. Iago and others come into the chamber and Emilia defends Desdemona's innocence. When the handkerchief is mentioned Emelia realizes that Iago is behind all of this. Othello sees the truth and tries to kill Iago. Iago kills Emilia and flees; Othello condemns himself and commits suicide. Iago is seized and taken away.