Near the walls of Peking
A mandarin reads a proclamation that the Princess Turandot will marry any man of royal rank who successfully answers three riddles propounded by her, but if he fails he must lose his head. The Prince of Persia, having just failed, will be beheaded at moonrise. The crowd is eager for the execution and nearly tramples underfoot the old blind Timur, deposed Tartar king, who is led by the slave girl Li, who cries to the crowd to take pity on him. Calaf, son of Timur, who had been separated from him in exile, recognises his father. Their joy at finding one another still alive is overshadowed by the continued persecution of the king who had defeated them, who is still pursuing Calaf. Li explains that she has guided Timur since his kingdom was lost, because once Calaf had smiled at her.
Although the people have been longing for the moon to rise and the execution to take place, when they see the young prince led to his death, their mood changes and they call for mercy. But Turandot appears on a balcony and signs for the execution to proceed. Calaf is struck by her beauty and, ignoring the warning of his father and Li, the arguments of the three courtiers Ping, Pang and Pong, and not even swayed by the dying cry of the Prince of Persia, strikes the gong as a signal of his challenge for the hand of the princess.
Scene 1: A pavilion in the palace grounds
Ping, Pang and Pong remember wistfully the peaceful retreats they have left to become courtiers under the cruel regime of Turandot. They express the hope that she will eventually yield to love and bring to an end the parade of executions, but they are brought back to the immediate prospect of another potential victim as the crowd gathers.
Scene 2: A vast square before the palace
The people hail the appearance of the emperor, who, weary of so much bloodshed, tries to dissuade Calaf from attempting the contest. But Calaf respectfully insists.
Turandot appears and, having explained that her aversion to men is based on the fate of a princess of her race who was violated and murdered by an invader, asks the riddles. Calaf successfully answers: Hope, Blood and Turandot. Turandot begs her father not to force her to marry the stranger, but he answers that he is bound by an oath. She tells Calaf that she will never be his, and he, touched by her distress, agrees to set her one riddle in his turn: if by dawn she can learn his name, he will die; if not, she must marry him. She consents, and the emperor hopes that at dawn Calaf will be his son-in-law.
Scene 1: The garden of the palace at night
Heralds proclaim that no one in the city shall sleep till the mystery of the unknown prince is solved. Calaf repeats their words, confident that by dawn he will have conquered and Turandot will be his. He is approached by Ping, Pang and Pong, offering beautiful girls, riches and glory if he will go away and leave them in peace. The people are angry with him because they are suffering on his account. Guards drag in Timur and Li, who have been seen with Calaf and are assumed to know his name. To save Timur, Li declares that she alone knows the secret and will not reveal it.
Turandot appears as the guards begin to torture Li and is unable to understand what gives her the strength to endure. Li answers that it is the power of love, which Turandot will soon feel herself. Seizing a knife from a guard, Li kills herself. Timur and the people, fearing that her offended spirit will seek revenge, pray to her ghost not to harm them, and even Ping, Pang and Pong feel something stirring in their long atrophied hearts.
The body of Li is carried out and Calaf and Turandot are left alone. He removes her veil and kisses her. With the first tears she has ever shed she confesses that she has feared and loved him since first seeing him. In response to her admission of defeat, he tells her his name.
Scene 2: Outside the palace
Turandot triumphantly announces to the emperor and assembled people that she knows the stranger's name: it is Love. Calaf and Turandot embrace and the emperor and people rejoice.