Scene i: The play begins in a street in Venice, a major Renaissance city-state where the first Act unfolds before the setting shifts to the island seaport of Cyprus under Venetian rule. On stage, we see the character of Roderigo, a young suitor for the hand of Desdemona, and that of Iago, a veteran officer under the command of Venice's military hero, the Moor Othello. Roderigo tells Iago that he is disturbed by the news that Othello, the middle-aged Moor, has just eloped with the much younger Desdemona, the daughter of Venetian senator Brabantio. Iago voices his own complaint about Othello, saying that the black hero-general has chosen Cassio, a junior in years to Iago, as his lieutenant, leaving Iago in the role of "ancient" and provoking his resentment. Iago openly allows that he will pretend to be loyal to Othello and then use his inside position to exact revenge. Together, the two go to the home of Desdemona's father, Brabantio, to tell him that his daughter has run away with an old black "ram" and to rouse his fatherly passions against Othello, a man to whom Brabantio had opened his house as a guest.

Scene ii: Shortly thereafter in another Venice street, Iago tells Othello that Brabantio has slurred the Moorish commander's honor, but Othello dismisses this, confident that his own military services to Venice "Shall out-tongue his complaints." Othello's young, second-in-command, the brilliant Michael Cassio arrives with word that the general has been summoned to the Duke of Venice's court to deal with an urgent military matter. Just then, Brabantio, Roderigo and some law officers come to take Othello to the Duke on the legal charges that he has enchanted and thereby abused Brabantio's daughter.

Scene iii: In the council-chamber of the Duke of Venice, we see the Duke and the senators of the city-state as they learn that the arch-enemies of Venice, the Turks, are now engaged in some aggressive but evasive actions toward either Rhodes or Cyprus. Their conversation is interrupted by an irate Brabantio who is escorted on stage by law officers and the object of his wrath, Othello. Although the Duke promises to punish the "beguiler" of Brabantio's daughter according to the law, he and the other Venetian leaders are taken aback when they learn that Brabantio's suit is against Othello, an invaluable military leader. Brabantio recounts how he invited the Moor to his home and says that his daughter must be under a spell to fall in love with a man of Othello's years and fearsome black visage. Othello defends himself: Desdemona was impressed by his stories of adventures and exploits, but her love for him involves no witchcraft. Desdemona then appears and confirms her authentic love for the Moor. Hearing this, Brabantio disowns his daughter and warns Othello about her capacity for deception. The Duke decrees that Othello will leave for Cyprus and its defense against the Turks; Iago will then escort Desdemona there to live with Othello as his lawful wife. On the side, Iago assures Roderigo that his scheme against Othello will leave Desdemona free to marry him, and he directs Roderigo to await further instruction and gather money to advance an emerging scheme against the Moor. On stage alone, Iago reiterates "I hate the Moor," and then targets Cassio, "a proper man" as an instrument through which he will gain his revenge against Othello.

Scene i: Now at the seaport of Cyprus (where the remainder of the play takes place), local officials report that a great storm has wracked the Turkish fleet. Cassio appears with further news: the Turks have been defeated but Othello's command ship may also have gone down. Iago arrives with Desdemona and his own wife, Emilia. When Othello arrives unscathed, he is given a fond welcome by all, but after the rest leave, Iago takes Roderigo aside and tells him that Othello's trusted lieutenant, Cassio, is in love with Desdemona. Iago takes Roderigo deeper into his machinations; while Cassio heads the guard that night, Roderigo will attack him so that, if Cassio reacts and leave his post, he may be charged with fighting on duty. This, Iago notes, would eliminate Cassio as Roderigo's other rival for Desdemona. After Roderigo agrees to this assignment, Iago remains alone on stage and tells us that he will corrupt Othello's mind against Cassio and Desdemona.

Scene ii: A one speech scene in which a herald announces that Othello, as the new governor of Cyprus, has proclaimed a holiday, a feast in celebration of his marriage to Desdemona and the Venetian victory over the Turks.

Scene iii: At the citadel of Cyprus, Othello, Desdemona and Cassio speak with each other, the Moor ironically commenting upon the "honesty" of Iago. Iago then arrives and encourages Cassio to join in the festive night's drinking, but Cassio says that only a little wine will make him drunk and unfit to supervise the watch. Iago cajoles him into drinking just "one cup" to the health of his general and Desdemona, and Cassio gets drunk before leaving for his duties. Iago dispatches Roderigo after Cassio to provoke a fight. When Othello appears he finds his second in command in complete disorder and dismisses Cassio from his post. Dismayed about his loss of honor and reputation, Cassio is consoled by Iago. The villain tells Cassio that he may be restored to his office if he persuades Desdemona to speak on his behalf to her husband Othello. The scene ends with Iago remaining on stage to tell us that when Desdemona shows her interest in Cassio's plight, this will advance his plan of making Othello uncontrollably jealous of his former lieutenant. Roderigo appears and Iago selectively tells him of the scheme ahead.

At one point, Othello reacts negatively to this line of suggestion, forcefully demanding that Iago give him "ocular proof" that Desdemona and Cassio are having an affair behind his back. At this juncture, however, Iago takes advantage of a simple mishap: Desdemona has lost a handkerchief given to her by Othello, and Iago's wife has found it. In what follows, Iago will plant this handkerchief in Cassio's quarters, using it as proof that the young lieutenant has been having a sexual affair with Othello's wife. At this point, Iago tells Othello that he has seen Cassio wipe his brow with the same handkerchief that the Moor gave to Desdemona. Faced with this proof, Othello is mad with rage and vows vengeance against Cassio and Desdemona while Iago pledges his assistance, saying that he will kill Cassio himself.

Scene iv: Othello finds Desdemona with Emilia and asks her to lend him the handkerchief that he gave to her, saying that it is precious, magical cloth given to him by his own mother. Desdemona cannot produce it (the handkerchief is under Iago's control), but she denies that it is lost. He becomes infuriated when the innocent Desdemona then takes up Cassio's suit again and leaves the stage in a rage. When Iago and Cassio then appear, Desdemona tells them that Othello is not himself, that "My lord is not my lord." Iago, knowing full well the cause of Othello's anger, volunteers to calm Othello down. After Desdemona and Emilia leave, Cassio's actual love interest, the courtesan Bianca appears and scolds the lieutenant for not seeing her of late.

Scene i: In front of his headquarters, Othello speaks with Iago, and the villain claims that he has overhead Cassio calling Desdemona's name while asleep. By now, Othello believes everything that Iago tells him, having become a "credulous fool, and he lapses into a trance. Cassio then arrives, and Iago sets him up by saying that he will speak with him later. His plan is to have Cassio talk to him about Bianca while an eavesdropping Othello thinks Cassio is referring to Desdemona. This ploy works, and Othello hears from Cassio directly about how "she" loves him. When Bianca arrives in person, the gist of the conversation only incriminates Cassio more for it seems that he has given Othello's handkerchief to Bianca, having received it himself from Desdemona. They leave the stage and Othello vows to kill Desdemona while Iago volunteers to be Cassio's "undertaker." Desdemona then enters with news from Venice: Othello has been recalled there and Cassio has been appointed to replace him as governor of Cyprus. Desdemona is pleased by these events, but a furious Othello physically strikes her. Iago tells the Venetian official Lodovico that Othello's brutality toward his wife is just one expression of the Moor's troubled mind and of their troubled marriage.

Scene ii: At his citadel, Othello talks with Emilia, and she assures him that she has never seen any sign that Desdemona has been an unfaithful wife to him. He nevertheless calls Desdemona to him and proceeds to call her a whore; she is completely befuddled by all this. Othello exits and Desdemona then explains her confusion to Emilia and her husband, Iago. When the two women depart, Roderigo arrives. He complains that while Iago has taken his money, he is no closer to gaining Desdemona's love than ever. Iago tells his pawn Roderigo that because Cassio has been named governor, Desdemona will be leaving for Venice. To prevent this, Iago proposes that Roderigo slay Cassio, forcing Othello and Desdemona to remain on Cyprus.

Scene iii: Othello orders Desdemona to go to bed and she obediently agrees. Emilia speaks briefly with Desdemona who says that she loves Othello dearly but now fears him. Emilia interprets this as a conventional abnormality, saying that all husbands are impossible.

Scene i: In a public street near Othello's citadel, Iago persuades Roderigo to murder Cassio; after his pawn exits, Iago considers the prospect of Cassio and Roderigo killing each other, thereby ending a dual threat to the exposure of his complex machinations. The two in fact duel and both men are seriously wounded, with Iago stabbing Cassio from behind in the confusion. Othello bursts upon the scene and when he hears Cassio's cries of distress, he believes that the trusty Iago has kept his word and done this task of revenge for him. When two government officials---Lodovico and Gratiano---arrive, Iago pretends to be an enraged witness of Roderigo's assault upon Cassio and then kills the wounded Roderigo before he can reveal Iago's true role. Bianca arrives, Iago intimates that this "notable strumpet" is somehow behind Roderigo's attack on Cassio, and takes her into custody.

Scene ii: The play's final, bloody scene opens in the bed chambers of Othello and Desdemona as the deranged Moor battles between his love for his beautiful young wife and his desire to murder her. When Desdemona appears, Othello's mind is fixed upon killing her. Othello reviews the evidence against Desdemona, including the visual proof of the mislaid handkerchief. She pleads that Cassio can explain what has occurred, but Othello tells her that Cassio has been slain (although Cassio has actually survived). She begs for mercy, but Othello smothers her with a pillow. Iago's wife, Emilia enters, and while she is there, Desdemona recovers enough to tell her lady-in-waiting that she is the innocent victim of her husband's jealousy. Desdemona dies and Othello tells Emilia that he has killed his wife because she committed adultery with Cassio. Emilia defends Desdemona and Othello reveals how Iago supplied him with evidence of her illicit love affair. Emilia is able to piece together all of the elements: she realizes that her husband Iago is the mastermind behind the entire vicious scheme. Othello cannot accept this, but cannot deny it either, and he falls on his bed overwhelmed by events and their true meaning in light of what Emilia has just disclosed about Iago. Several officials, including Gratiano and Montano, arrive with Iago. Emilia immediately accuses her husband of villainy, Othello runs at Iago and Iago stabs his wife, flees, and is chased by Montano and some others. They catch him, and a wounded Cassio also enters with Iago in chains. Othello wounds, but does not kill Iago, lashes out at Lodovico who strips him of his governorship, and then stabs himself to death. At the end, Lodovico standing beside the wounded Cassio tells Iago that his part in this mayhem is plain and that he will soon be transported to torture and execution.