Radamès, an officer in the Egyptian army, learns that rival forces are advancing on his city. If he can lead the troops in a conclusive victory for Egypt, he speculates, the king will allow him the prize he seeks: Aida. Currently enslaved to the Egyptian princess Amneris, Aida is the daughter of Amonasro, who is leading the attack on Egypt. For her own safety, Aida is keeping her identity, as well as her feelings for Radamès, under wraps. When Radamès is named commander of the Egyptian army, Aida is distraught: the upcoming battle will pit her lover against her father.
The Egyptian princess Amneris is also in love with Radamès, although he is indifferent to her. Suspicious, Amneris tricks Aida into revealing her feelings for the Egyptian commander. Meanwhile, Radamès leads the Egyptians to victory. When they return, Amonasro, Aida’s father, is among the prisoners of war. Aida rushes to greet him; he cautions her not to reveal their royal identity. Amonasro then eloquently pleads with the Egyptians for clemency. Radamès is in favor of granting Amonasro’s request, but Ramfis, the Egyptian high priest, disagrees. After hearing both sides, the Egyptian king revokes Amonasro’s death sentence, but keeps him in custody. The king declares that the victorious Radamès will be granted the hand of his daughter, Amneris, in marriage — an offer he cannot safely refuse.
Aida, preparing for a secret assignation with Radamès, is surprised by her father, who asks her to obtain strategic information from her lover. Initially she refuses, but Amonasro appeals to her loyalty and patriotism. When Radamès appears, Aida manipulates him into revealing the Egyptian army’s plans. Amonasro emerges from his hiding-place, triumphant, and Radamès is distraught over his unwitting treachery. He surrenders himself to Ramfis, the high priest. Amneris offers to save his life if he will renounce Aida, but Radamès is firm in his love. Condemned to death, he prepares to spend his last moments in solitude. But Aida finds her way to him — if she cannot share her life with Radamès, she will die with him so they can be together for all eternity.