Norwegians, aided by Scottish rebels, have invaded Scotland. The Scots successfully defend their country and their beloved king, Duncan. One Scotsman in particular, Macbeth, Thane of Glamis, distinguishes himself in fighting off the invaders. After the battle, Macbeth and his friend Banquo come upon the weird sisters, three witches who prophesy that Macbeth will become Thane of Cawdor, and one day King. They further prophesy that Banquo's descendants will be kings. The men don't at first believe the witches, but then learn that the old Thane of Cawdor was actually a traitor helping the Norwegians, and that Duncan has rewarded Macbeth's bravery on the battlefield by making him Thane of Cawdor. Macbeth immediately fantasizes about murdering Duncan and becoming king, but pushes the thought away. Later that day, Duncan announces that his eldest son, Malcolm, will be heir to his throne. As Macbeth begins to succumb to his ambition, Duncan decides to spend the night in celebration at Macbeth's castle of Inverness.
Lady Macbeth receives a letter from her husband about the prophecy and Duncan's imminent arrival. She decides her husband is too kind to follow his ambitions, and vows to push him to murder Duncan and take the crown that very night. Macbeth at first resists his wife's plan, but his ambition and her constant questioning of his courage and manhood win him over. That night they murder Duncan and frame the men guarding Duncan's room. The next morning, Macduff, another Scottish thane, discovers Duncan dead and raises the alarm. Macbeth and Lady Macbeth pretend to be shocked and outraged. Macbeth murders the guardsmen of Duncan's room to keep them silent, but says he did it out of a furious rage that they killed the king. Duncan's sons think they may be the next target, and flee. Macbeth is made king, and because they ran, Duncan's sons become the prime suspects in their father's murder.
Because he knows the witches' prophecy, Banquo is suspicious of Macbeth. And because of the prophecy that Banquo's line will reign as kings, Macbeth sees Banquo as a threat. Macbeth gives a feast, inviting many thanes, including Banquo. Macbeth hires two murderers to kill Banquo and his son Fleance as they ride to attend the feast. The men kill Banquo, but Fleance escapes. At the feast, Macbeth sees Banquo's ghost, though no one else does. Macbeth's behavior and the death of Banquo make all the thanes suspicious. They begin to think of Macbeth as a tyrant. Macduff refuses to appear at the royal court at all, and goes to England to support Malcolm in his effort to raise an army against Macbeth.
Macbeth visits the three witches to learn more about his fate. They show him three apparitions who tell Macbeth to beware Macduff, but also that no "man born of woman" can defeat him and that he will rule until Birnam Wood marches to Dunsinane (a castle). Since all men are born of women and trees can't move, Macbeth takes this to mean he's invincible. Yet the witches also confirm the prophecy that Banquo's line will one day rule Scotland. To strengthen his hold on the crown, Macbeth sends men to Macduff's castle to murder Macduff's family. Meanwhile, in England, Macduff and Malcolm prepare to invade Scotland. When news comes to England of the murder of Macduff's family, Macduff, weeping, vows revenge.
While the English and Scottish under Malcolm march toward Dunsinane, Lady Macbeth begins sleepwalking and imagining blood on her hands that can't be washed off. Macbeth has become manic, cruel, and haughty—many of his men desert to Malcolm's side. In Birnam Wood, Malcolm and his generals devise a strategy to hide their numbers—they cut branches to hold up in front of them. As Macbeth prepares for the siege, Lady Macbeth dies, perhaps of suicide. Macbeth can barely feel anything anymore, and her death only makes him give a speech about the meaninglessness of life. Then Malcolm's forces appear looking like a forest marching toward the castle. Malcolm's forces quickly capture Dunsinane, but Macbeth himself fights on, mocking all who dare to face him as "men born of woman." But Macduff reveals that he was "untimely ripped" from his mother's womb (a caesarean section). Macduff kills Macbeth, and Malcolm is crowned as King of Scotland.