The second act opens with a stately march, introducing the messengers of peace, who join in a chorus of greeting, followed by a second chorus of senators and the tender of submission made by the nobles. A terzetto between Adriano, Orsini, and Colonna, set off against a chorus of the nobles, leads up to the finale. It opens with a joyful chorus ("Erschallet feier Klaenge"), followed by rapid dialogue between Orsini and Colonna on the one hand and Adriano and Rienzi on the other. A long and elaborate ballet intervenes, divided into several numbers,—an Introduction, Pyrrhic Dance, Combat of Roman Gladiators and Cavaliers, and the Dance of the Apotheosis, in which the Goddess of Peace is transformed to the Goddess, protector of Rome. The scene abruptly changes, and the act closes with a great ensemble in which the defiance of the conspirators, the tolling of bells, the chants of the monks, and the ferocious outcries of the people shouting for revenge are mingled in strong contrasts.
The third act is full of tumult. After a brief prelude, amid the ringing of bells and cries of alarm, the people gather and denounce the treachery of the nobles, leading up to a spirited call to arms by Rienzi ("Ihr Roemer, auf"). The people respond in furious chorus, and as the sound of the bells and battle-cries dies away Adriano enters. His scene opens with a prayer ("Gerechter Gott”) for the aversion of carnage, which changes to an agitated allegro ("Wo war ich?”) as he hears the great bell of the Capitol tolling the signal for slaughter. The finale begins with a massive march, as the bells and sounds of alarm are heard approaching again, and bands of citizens, priests and monks, the high clergy, senators and nobles, pass and repass in quick succession, at last followed by Rienzi, which is the signal for the great battle-hymn, “Santo spirito cavaliere,” which is to be sung with great fire and energy, accompanied by great and small bells ringing behind the scenes, the clash of swords upon shields, and full power of chorus and orchestra. A dialogue follows between Adriano and Rienzi, and then the various bands disappear singing the ritornelle of the hymn. A great duet ("Lebwohl, Irene”) ensues between Adriano and Irene, which in its general outlines reminds one of the duet between Raoul and Valentin in “The Huguenots.” At its conclusion, after a prayer by the chorus of women, the battle hymn is heard again in the distance, gradually approaching, and the act closes with a jubilee chorus ("Auf! im Triumpf zum Capitol"), welcoming the return of the conquerors.