A Roman officer betrayed by the emperor leads a gladiator's rebellion.

In a bleak winter forest in the year 180 A.D., Roman general Maximus Decimus Meridias reviews his battle-weary troops before they launch their final campaign to conquer Germania. Maximus is greatly admired by his men, alongside whom he fights during the battle and leads them to victory. Commodus and his sister Lucilla, the scions of Emperor Marcus Aurelius, travel to Maximus' army camp, having been summoned by their father. On their arrival they learn that the soldiers have been gone for nineteen days. Commodus rides to the front to honor his father but is affronted when Marcus Aurelius pays homage to Maximus. The emperor, who loves Maximus as a son, believes that he is slowly dying and sends for Maximus that night to ask him to succeed him after his death and give the control of Rome to the Senate. Maximus, longing only to return to his native Spain and his family, rejects the idea, but Marcus Aurelius is adamant as he believes that Commodus is morally corrupt. While Maximus prays alone to devotional figures of his family for guidance, Marcus Aurelius tells Commodus his decision. Commodus feels betrayed and, sobbing, murders his father. The murder is covered up and Commodus immediately seizes power. When Maximus refuses to vow his loyalty, Commodus orders his immediate execution. In a remote forest location, Maximus overwhelms his would-be assassins and, injured, rides for home, but arrives to find that his wife and son have been hanged and burned to death by Commodus' Praetorian guards. Maximus collapses and while unconscious is taken prisoner by a slave trader. A fellow captive named Juba befriends Maximus and treats his wound, after which they are both sold to fight promoter Proximo to be trained as gladiators. Proximo assumes that Maximus is a deserter from the Roman army and he is dubbed "Spaniard." While a reluctant Maximus is being trained as a gladiator, Commodus returns to Rome as emperor but is uninterested in the actual work of ruling. Lucilla acts as a mediator between Commodus and the hostile Senate, while Commodus focuses on his plans to hold 150 days of games to honor his father. In time, Maximus gains the respect of his fellow gladiators as well as the crowds who cheer him on as he repeatedly defeats his foes, but Maximus remains disgusted by the blood sport. Proximo meets privately with Maximus and admits that he was once a gladiator who was granted his freedom by Marcus Aurelius. Proximo informs him that they will be fighting in Commodus' games at the Roman coliseum and advises him that if he wins that crowd, he, too, might win his own freedom. Meanwhile, Lucilla, a widow who was once in love with Maximus, tries to keep her brother from dissolving the Senate, resorting even to sleeping tonics to keep him at bay. Proximo and his gladiators arrive in Rome and are assigned to fight a re-creation of the Battle of Carthage. The gladiators are awed by the size of the coliseum but once inside the arena, they battle for their lives. Maximus uses his skills as a general and urges his fellow gladiators to work together, and they succeed in killing the opposition. The audience cheers them on and, when Commodus goes down to meet the gladiators, he demands that Maximus remove the helmet that hides his face. Maximus then reveals his true identity and vows vengeance, but when the frightened Commodus calls forth his Praetorian guards, the crowds boo him until he gives Maximus the thumbs-up symbol of approval. Commodus later confides to Lucilla that his guards lied to him that Maximus was dead and that this must mean he does not have their respect. Lucilla advises him to force them to respect him, but later secretly meets with Maximus to seek his help against Commodus, whom she fears. Maximus is too embittered to offer his support. In an attempt to kill Maximus, Commodus next pits him against several vicious tigers and a top gladiator; although Maximus again survives, he refuses to kill the gladiator. Maximus' former assistant, Cicero, makes contact with him and Maximus sends him to Lucilla to tell her he has changed his mind and will help her. When Lucilla arranges for Maximus to meet with Gracchus, a Roman senator who opposes Commodus, Maximus relates to Gracchus that it was Marcus Aurelius' final wish that power be returned to the Senate. Maximus then asks for his freedom, in return for which he will gather his troops and kill Commodus and his guards. When Gracchus is arrested soon after, Lucilla arranges with Proximo to free Maximus that night. At the palace, Commodus is stunned when Lucilla's son Lucius innocently reveals that his mother believes that Maximus is the savior of Rome. Lucilla returns as Commodus is telling Lucius a story about ancestral betrayal, and she realizes that her disloyalty has been discovered. As a result, Commodus' spies slip a poisonous snake into the bed of senator Gaius, who is sympathetic to Lucilla's cause. Before Maximus can be freed, Commodus' Praetorian guards arrive at Proximo's encampment. After giving Maximus the keys to free all the slaves, Proximo fights the Praetorians to his death. The slaves rally to combat the guards while Maximus escapes to meet Cicero. Maximus finds Cicero at the appointed place seated on his horse, but Cicero cries out a warning and is hanged by a noose around his neck, while Maximus is captured Commodus' forces. Commodus now demands that Lucilla live estranged from her son, and implies that he hopes that he and she will produce their own heir. He then decides to fight Maximus himself as part of the games, but to ensure his own victory, stabs the former general in the back, and then has his man, Quintus, cover the wound with armor. Commodus and Maximus face off in the arena, but when Commodus loses his sword, Quintus refuses to give him another. Commodus then pulls a knife from his sleeve and they fight hand-to-hand, but Maximus overpowers him and finally gains his revenge, killing Commodus. As Maximus slowly dies from the knife wound, he tells Quintus to free his men, reinstate Gracchus and restore the dream of Rome as Marcus Aurelius had wished. After Lucilla runs to his side and assures him that Lucius is safe, Maximus dies with visions of his family walking through fields to greet him. Lucilla weeps over his body, then demands that the people of Rome honor him. Gracchus and the slaves carry Maximus' body from the arena, leaving Commodus in the dirt. Later, Juba buries the carved devotional figures of Maximus' family, and having earned his own freedom, pledges to see his friend again in time.