- 1871 - Grand opéra Dances and music to celebrate Radames' victory take place. However, Amneris is still in doubt about Radames' love and wonders whether Aida is in love with the young warrior. She tries to forget her doubt, entertaining her worried heart with the dance of Moorish slaves.
When Aida enters the chamber, Amneris asks everyone to leave. By falsely telling Aida that Radames has died in the battle, she tricks her into professing her love for him. In grief, and shocked by the news, Aida confesses that her heart belongs to Radames eternally.
This confession fires Amneris with rage, and she plans on taking revenge on Aida. Ignoring Aida's pleadings, Amneris leaves her alone in the chamber.
Scene 2: The grand gate of the city of Thebes
Radames returns victorious and the troops march into the city. The Egyptian king decrees that on this day the triumphant Radames may have anything he wishes. The Ethiopian captives are rounded up and Amonasro appears among them. Aida immediately rushes to her father, but their true identities are still unknown to the Egyptians. Amonasro declares that the Ethiopian king (he himself) has been slain in battle. Aida, Amonasro and the captured Ethiopians plead with the Egyptian King for mercy, but the Egyptians call for their death.
As his reward from the King, Radames pleads with him to spare the lives of the prisoners and to set them free. Gratefully, the King of Egypt declares Radames to be his successor and to be his daughter's betrothed. Aida and Amonasro remain as hostages to ensure that the Ethiopians do not avenge their defeat.