In Gaul at the time of the Roman occupation.
Act I
In the sacred forest of the druids at night. The high priest Oroveso and the druids invoke the gods for a sign to be given to them to make war on the Romans. Pollione, proconsul Roman, confides to his friend Flavius that he no longer loves Norma, who has, however, broken her vows of chastity for him and gave him two children. He is now in love with another priestess, Adalgisa, and fears the vengeance of Norma.
Norma invokes the gods and, to protect Pollione, announces that the time has not yet come to wage war against the Romans. Adalgise, who thinks she is alone, reveals the secret of her love for Pollione, who hears her and offers for her to flee with him to Rome, which she accepts.
Norma’s residence. Adalgise, before leaving, confesses to Norma that she has fallen in love with a Roman. As this story resembling hers, Norma does not have the courage to condemn her, but she ends up understanding that the man Adalgise has fallen for is Pollione. Norma's anger explodes and Adalgise ends up giving up fleeing with Pollione.
Act II
Norma’s residence. It's night, the two sons of Norma and Pollione are sleeping. She is tempted to kill her children to hurt Pollione by destroying what is dearest to him but she can not. She comes to accept that Pollione and Adalgise live out their love but wants the latter to become a mother to her children. The young priestess does not want to betray Norma, she will go to Pollione only to remind him of his obligations in marriage. Moved by Adalgise’s renunciation, Norma promises her eternal friendship.
Near the wood of the druids. Gallic warriors invoke war. Norma is waiting for the return of Adalgise but learns that she has failed. Norma's anger is enflamed; she warns the warriors that it is time for war against the Romans. Rumor has it that a Roman has entered the temple to kidnap a priestess: indeed, it was Pollione, who tried to kidnap Adalagise. Norma begs him one last time, threatening to reveal the betrayal of Adalgise to the Gallic people. Against all odds, she incrimates herself in front of the crowd, and thereby condemning herself to death. Shocked by her gesture, Pollione asks her pardon and follows her in death.
