At the age of fifteen, Marozia became the mistress of Theophylact's cousin Pope Sergius III, whom she knew when he was bishop of Portus.

That, at least, is the story found in two contemporary sources, the Liber Pontificalis and the Antapodosis sive Res per Europam gestae (958–62), by Liutprand of Cremona (c. 920–72).

By the time Alberic I was killed at Orte in 924, the Roman landowners had won complete victory over the traditional bureaucracy represented by the papal curia.

In order to counter the influence of Pope John X (whom the hostile chronicler Liutprand of Cremona alleges was another of her lovers), Marozia subsequently married his opponent Guy of Tuscany.

Her descendants remained active in papal politics, starting with Alberic II's son Octavian, who became Pope John XII in 955.