Inside the temple of Solomon
The Assyrian king, Nabucco (Nebuchadnezzar) of Babylon, is rapidly advancing with his army toward the temple of Solomon. Within the temple walls, the Hebrews beg their god, Jehovah, not to let them fall prey to Nabucco (Chorus: Gli arredi festivi). The prophet Zaccaria brings in Nabucco’s daughter, Fenena, who is his hostage. Ismaele rushes in and announces that Nabucco has entered the city. Zaccaria entrusts Fenena to Ismaele, as he prepares for the final battle.
Fenena and Ismaele recall the time when Ismaele – as ambassador of Judea – was imprisoned in Babylon. Fenena rescued him, undeterred by the jealousy of her sister Abigaille, who loves Ismaele as well. Ismaele vows to free Fenena, although he would have to betray his own religion. Abigaille invades the temple at the head of a group of warriors. She taunts the lovers bitterly, but then, turning to Ismaele, reminds him that if he loved her, she could save his people (Trio: Io t’amavo!).
Just after the horrified Hebrews rush in, Nabucco arrives in triumph. Confronting an outraged Zaccaria, the king vows to destroy the Hebrews. Zaccaria threatens to kill Fenena, but Ismaele disarms him. Nabucco orders the temple sacked and burned. Zaccaria calls on Jehovah to punish Ismaele for betraying his people.