Gaul during the Roman occupation. Pollione, the Roman consul, has abandoned Norma, the Druid high priestess (by whom he has two sons) in favour of Adalgisa, an acolyte. Norma is unaware of Pollione's infidelity.
Despite ominous dreams, Pollione decides to take Adalgisa back to Rome and marry her. Norma is shattered to discover that Adalgisa's lover is none other than Pollione, while Adalgisa is horrified to learn that Pollione is intending to abandon Norma.
Norma wrestles with her conscience as she contemplates the murder of her children. She manages to restrain herself and decides to entrust them to Adalgisa's care.
Adalgisa renounces Pollione to Norma and, swearing never to love him again, promises to persuade him to return to the mother of his children.
When Norma learns of Adalgisa's failure to achieve this goal, she incites the Gauls to war against the Romans: all that is needed is a sacrifice.
Pollione is captured breaking into the virgin's temple and is sentenced to death, but he still refuses to disown Adalgisa.
Norma, driven to despair, orders the funeral pyre to be lit - she will take Pollione's place as the sacrifice. Her selflessness forces Pollione to reconsider and he realizes that he does in fact love Norma after all.
But it is too late: after consigning her children to her father's care, she mounts the pyre, where she is joined in death by Pollione.