War has broken out between the Babylonians and the Hebrews. The Hebrews have captured Fenena, younger daughter of the Babylonian king Nabucco and are holding her hostage. Nabucco has sworn to conquer Jerusalem.

PART I

The Hebrews pray for mercy as the Babylonians advance. The prophet Zaccaria reminds them of God’s power. The Hebrews go into battle. Ismaele, nephew of the King of Jerusalem, remains behind to guard Fenena. Fenena and Ismaele recall how they fell in love while Ismaele was a prisoner of the Babylonians, and how Fenena helped him to escape. They are interrupted by Abigaille, who also loves Ismaele. Abigaille vows vengeance on the lovers.The defeated Hebrews rush in, followed by Nabucco and his triumphant warriors. Zaccaria threatens to kill Fenena. Fearful for Fenena, Ismaele disarms him. The crowd curse Nabucco as the Babylonian king orders the destruction of the Temple.

PART II

Nabucco has brought many Hebrews as prisoners to Babylon. Meanwhile, Abigaille has stolen a document that proves her true parents were slaves: she was only fostered by Nabucco. She broods on her loneliness and Nabucco’s preference for Fenena. When the High Priest of Baal informs her that Fenena is freeing the Hebrews, Abigaille decides to take control of the kingdom. Zaccaria prays, then goes to find Fenena. Ismaele is accused of treachery by a group of Levites. Zaccaria returns with Anna and Fenena, and Anna informs the Levites that Fenena has converted to Judaism and is now their ally. She urges the Levites to forgive Ismaele. Abdallo announces the rebellion set in motion by Abigaille. Abigaille and the High Priest enter in triumph. Nabucco challenges Abigaille to take the crown from him. He defiantly declares that he is no longer a king, but indeed a god, then suddenly collapses. As he raves in debilitating confusion, Abigaille claims the crown.

INTERVAL

PART III

The Babylonians celebrate their victory. Abigaille tricks Nabucco, who doesn’t recognize her, into signing a death warrant for the Hebrews. Once he has signed, Abigaille gleefully tells him that he has condemned Fenena. Furious, Nabucco regains enough sanity to recognize Abigaille. He tells her that she is the child of slaves. Abigaille destroys the stolen document that would prove it. Nabucco begs her for mercy but she is adamant that the Hebrews must die, and orders Nabucco to be imprisoned. The Hebrews mourn their exile in Babylon. Zaccaria prophesies that Babylon will be destroyed and his people will be free. His words give the Hebrews courage.

PART IV

Nabucco raves about the war and the defeat of Jerusalem, echoing the prophecy made by Zaccaria to the Hebrews. He hears voices crying for the execution of Fenena but is powerless to help her. In despair, he prays to the God of the Hebrews, vowing that he will convert if God will save Fenena. His sanity is immediately restored, and his servant Abdallo enters with soldiers to release him. Nabucco leads his men out to free the Hebrews. The Hebrew prisoners are led in to be sacrificed and Fenena prepares serenely for death. Nabucco and his army enter and free the prisoners. Everyone joins in a prayer. Abigaille stumbles in. Having poisoned herself, she prays for God’s mercy, collapsing as Zaccaria hails Nabucco king under God.