Following the assassination of Julius Caesar and the battle of Philippi, Mark Antony, Octavius Caesar and Lepidus are the joint rulers of the known world.

Antony, however, is captivated by Cleopatra, Queen of Egypt, and is neglecting his military responsibilities to spend time with her at her court in Alexandria, where they live a life of luxary and self-indulgence. This scandal is now the talk of Rome and has created a dangerous rift between Antony and young Octavius Caesar.

News comes from Rome that Fulvia, Antony's wife, is dead. More urgently, the power of the triumvirate is being challenged by Pompey, son of Julius Caesar's former rival, Pompey the great. Antony is forced to return to Rome and resume his responsibilities. When it is suggested that he should cement the alliance with Octavius by marrying his sister, Octavia, Antony agrees. His friend and comrade-in-arms Enobarbus, however, predicts that Antony will not be able to break with Cleopatra. Back in Egypt, the news of Antony's marriage sends Cleopatra into a jealous tirade.

On the brink of war, Antony and Octavius make peace with Pompey and celebrate the treaty with a feast. Shortly afterwards, however, Antony learns that not only has Octavius attacked Pompey after all, but he has also spoken scornfully of Antony in public and has had Lepidus imprisoned on dubious charges. Antony sends Octavia back to negotiate with her brother while he returns secretly to Alexandria.

News arrives in Rome that Antony and Cleopatra have crowned themselves and their children kings and queens in Alexandra. Antony's desertion of Octavia is the final straw. Octavius declares war on Egypt.

The Egyptian forces lose the sea-battle of Actium when Antony deserts the battle to follow Cleopatra's fleeing ship. Antony is consumed with shame and despair. However, hearing that Octavius has offered to make a secret treaty with Cleopatra, he rouses himself for a second, victorious battle.

On the eve of the third battle, Antony's soldiers are nervous and fear bad omens. Even the faithful Enobarbus deserts him for Octavius.

In the event, the Egyptian fleet surrenders and Antony, in his fury, accuses Cleopatra of betraying him to Octavius. She retreats from his anger to her monument and, hoping to bring him round, sends a false report that she is dead. On hearing this, however, Antony attempts suicide and is brought to Cleopatra's monument to die in her arms. Rather than be captured and enslaved by the Romans, Cleopatra also kills herself, using a poisonous snake brought to her concealed in a basket of figs.

With all his enemies eliminated, Octavius returns victorious to Rome.