In the act before this aria, Calaf has correctly answered the three riddles put to all of Princess Turandot's prospective suitors. Nonetheless, she recoils at the thought of marriage to him. Calaf offers her another chance by challenging her to guess his name by dawn. As he kneels before her, the "Nessun dorma" theme makes a first appearance, to his words, "Il mio nome non sai!" (My name you do not know!). She can execute him if she correctly guesses his name; but if she does not, she must marry him. The cruel and emotionally cold princess then decrees that none of her subjects shall sleep that night until his name is discovered. If they fail, all will be killed.

As the final act opens, it is now night. Calaf is alone in the moonlit palace gardens. In the distance, he hears Turandot's heralds proclaiming her command. His aria begins with an echo of their cry and a reflection on Princess Turandot:

Nessun dorma! Nessun dorma! Tu pure, o Principessa, nella tua fredda stanza, guardi le stelle che tremano d'amore, e di speranza!	None shall sleep! None shall sleep! Not even you, oh Princess, in your cold bedroom, watching the stars that tremble with love, and with hope!
Ma il mio mistero e chiuso in me; il nome mio nessun sapra! No, No! Sulla tua bocca, lo diro quando la luce splendera!	But my secret is hidden within me; no one will know my name! No, no! On your mouth, I will say it when the light shines!
Ed il mio bacio sciogliera il silenzio che ti fa mia!	And my kiss will dissolve the silence that makes you mine!

Just before the climactic end of the aria, a chorus of women is heard singing in the distance:

Il nome suo nessun sapra, E noi dovrem, ahime, morir, morir!

No one will know his name, and we will have to, alas, die, die!

Calaf, now certain of victory, sings:

Dilegua, o notte! Tramontate, stelle! Tramontate, stelle! All'alba, vincero! Vincero! Vincero!

Vanish, o night! Fade, you stars! Fade, you stars! At dawn, I will win! I will win! I will win!