Act I
It is the eve of the marriage of Radamès and Amneris. Captain Radamès of the Egyptian army is in love with Aida, an Ethiopian slave serving the king's daughter Amneris. When Aida and Amneris arrive at the court, Amneris, who herself hopes to marry Radamès, suspects there is something going between the Captain and her slave. She is right. The king arrives to announce that Radamès has been chosen to command the army in the battle against Ethiopia, and Aida is torn between love for her country and for Radamès.

Radamès receives the sacred sword in a grand ceremony in the temple of Vulcan.

Act II
Amneris is determined to discover the real nature of Aida's feelings for Radamès. When she falsely announces Radamès' death, the slave girl cries out in despair. Amneris is convinced that Aida is her rival, and vows revenge.

The Egyptian army parades triumphantly before the king to celebrate their victory over Ethiopia. Radamès asks for mercy for the Ethiopian prisoners, among whom is Amonasro, Aida's father. The king agrees, but decides to keep Aida and her father as hostages.

Act III
It is the eve of the wedding of Radamès and Amneris.

Amonasro has found out about the love between his daughter and Radamès, and orders her to ask Radamès about the Egyptian army's plans. At their secret tryst Radamès reveals to Aida that the Egyptian army will attack the Ethiopians at the Napata Pass. Amonasro, who has been listening secretly, emerges from his hiding place, exultant. Radamès realises he has unwittingly betrayed his own country. When Amneris and the high priest arrive he gives himself up.

Act IV
Amneris begs Radamès to forsake Aida but Radamès declares himself unable to live without his beloved Aida. He is ready to pay for his crime. The priests' tribunal condemns him to being buried alive.

Act V
The priests seal the crypt below the Temple of Vulcan, with Radamès inside. Suddenly Aida appears; she has hidden in the crypt in order to be with him to the last. They await their death together, while Amneris, in the temple above, cries her lament.