Act One
Oroveso, the Chief Druid and Norma’s father, asks the Gallic warriors to beat the gong as soon as the moon rises. This is the signal for his daughter to perform the rite in the sacred grove, where she can also fathom the will of Irminsul, god of war. The men want Norma at last to give the signal to rebel against the occupying Roman forces.
The Roman proconsul Pollione, Norma’s secret husband and father of her two children, reveals to his friend Flavio that he has fallen in love with another, younger priestess, Adalgisa. He tells Flavio about a vision he had of Norma’s revenge taking him by surprise at his wedding to Adalgisa in Rome. – The druids’ sacred gong resounds, and Norma is called into the grove. Flavio warns of the mortal danger threatening any unbeliever who is found in the forest. Pollione affirms that he will vanquish the gods of the Gauls for the sake of his love for Adalgisa.
The Gauls gather in order to hear the god Irminsul’s orders from the mouth of their seer, Norma. She opposes their calls for war, as the enemy is in a stronger position, and prophesies that Rome will one day perish, a victim of its own vice. She then invokes the goddess of the moon, asking her to lend weight to her appeals for peace. The people join in her prayer. Norma still intends to protect Pollione, but has not failed to notice that his love for her has diminished.
At the altar after all have left, Adalgisa implores Irminsul to help her resist the temptation to which she is subjected by an unknown Roman, whom she has been meeting secretly in the forest for some time. Pollione appears and urges her to go to Rome with him as his wife. She can no longer suppress her feelings and promises to break her priestess’s vows and flee with him the next morning.
In Norma’s house, her confidante Clotilde is looking after her two children. Norma has felt ambivalent towards them since finding out that Pollione has been recalled to Rome; until now he has not revealed to her whether he intends to take her with him. – Clotilde hides the children from Adalgisa, who has come to talk to Norma in confidence. The novice confesses that she has fallen in love and asks Norma either to release her from her vows or to help her to overcome her forbidden love. Adalgisa’s account reminds Norma of her own encounter with Pollione. She promises Adalgisa that she will be happy with her lover.
Just as Norma asks the lover’s name, Pollione appears. When Adalgisa learns that he is not only Norma’s husband, but has also had children with her, she turns away from him in horror. While Norma curses him, Pollione insists that his love for Adalgisa is stronger than anything else. The singing of the Gauls, far off, calling the priestess to return to the altar of Irminsul, mingles with Norma’s oaths of vengeance.

Act Two
Norma approaches her two sleeping children with a dagger. Without Pollione’s help she can no longer protect them from her own people; on the other hand, she does not want to allow them to become the slaves of a stepmother in Rome. However, she cannot bring herself to kill her children. She orders Clotilde to call Adalgisa. Norma announces to her that she intends to atone for her own misdeeds by committing suicide and to entrust the children to her rival. Yet Adalgisa will hear nothing of a union with Pollione. In­stead, she suggests going to the Roman camp in order to persuade him to return to Norma. The two women swear eternal friendship.
The warriors meet in the forest in secret to discuss how they should act in the knowledge that Pollione has been recalled to Rome. Oroveso joins them and reports that Pollione is to be succeeded by an even crueller military leader. However, as long as Irminsul does not give his consent, through Norma, to their launching an attack, the men are con­demned to silence. They decide to pretend to be peaceable in order to strike even more effectively when the time comes.
Just as Norma is indulging in new hopes, Clotilde brings her a message from Adalgisa: Pollione has no intention of returning to her. Far from it – he swears to abduct Adalgisa from the altar. Now Norma’s fury knows no bounds. She beats the sacred gong and demands that the people who come running intone the chants of war. Clotilde reports that a Roman has been captured in the sacred grove; it is Pollione. He refuses to answer Oroveso’s questions, instead asking to be put to death. Norma steps forward and takes the sacrificial knife. However, she changes her mind and sends everyone away – explaining that she must first discover with whom the evil-doer is in league.
One last time, Norma beseeches her faithless husband to forsake Adalgisa; under this condition she will save his life and then part from him for ever. When he refuses, she tells him how she has already been on the point of killing their two children. Now Pollione’s death is no longer enough for her: all Romans shall pay for his disloyalty with their lives – and so shall Adalgisa, whose forbidden love she will report to the Gauls.
Norma announces to the people assembled that a new victim for Irminsul’s blood lust has been found: a priestess who has betrayed her vows and colluded with the enemy. However, she does not mention Adalgisa’s name, but accuses herself of the crime. Oroveso is as horrified as all the others present. Pollione now once again acknowledges Norma and asks her for forgiveness. He wants to die with her, united in love. Norma forces her father to promise to adopt her children – conceived against the divine law. Now she is ready to mount the pyre.