His tenure was part of a period of feudal violence and disorder in central Italy, when the Papacy was a pawn of warring aristocratic factions. It was also the dawn of an age of powerful women. Sergius was the son of Benedictus, and came from a noble Roman family.
The pontificate of Sergius III, according to Liutprand of Cremona, was remarkable for the rise of what papal historians saw as a "pornocracy," or rule of the harlots, a reversal of the natural order as they saw it, according to Liber pontificalis and a later chronicler who was also biased against Sergius III. This "pornocracy" was an age with women in power: Theodora, whom Liutprand characterized as a "shameless whore... [who] exercised power on the Roman citizenry like a man" and her daughter Marozia, the mother of Pope John XI (931–935) and reputed to be the mistress of Sergius III, largely upon a remark by Liutprand (see Brook link below).
Sergius III owed his rise to the power of his patron, the military commander Theophylact, Count of Tusculum who held the position of vestarius in control of the disbursements at the top of papal patronage. Sergius III and his party opposed Pope Formosus (891–896), who ordained him bishop of Caere (Cerveteri) – in order to remove him from Rome, as an unsympathetic source records. He was his faction's unsuccessful candidate for the papacy in 896; when Pope John IX (898–900) was elected instead, he excommunicated Sergius III, who had to withdraw from his see at Cerveteri for safety. Elected Pope in 897, Sergius III was forcibly exiled by Lambert, duke of Spoleto, and all the official records were destroyed; consequently most of the surviving documentation about Sergius comes from his opponents.
When antipope Christopher (903–904) seized the seat of St. Peter by force, the Theophylact faction of Romans revolted and ejected him in 903–904. They then invited Sergius III to come out of retirement. His return is marked as January 29 904.
Back in power, Sergius III now annulled all the ordinations of Formosus and demanded all bishops ordained by Formosus be reordained, an unwelcome decision reversed again after his death. Sergius III honoured Pope Stephen VI (896–897), who had been responsible for the "Cadaver Synod" that had condemned and mutilated the corpse of Pope Formosus, and placed a laudatory remark on Stephen VI's tombstone. He then reportedly had the much-abused corpse of Formosus exhumed once more, tried, found guilty again, and beheaded, thus in effect conducting a second Cadaver Synod, although Joseph Brusher, S.J. says that "Sergius [III] indulged in no resurrection-man tactics himself and Schaff, Milman,, Gregorovius, von Mosheim, Miley, Mann, Darras, John the Deacon of Naples, Flodoard, and others make no mention of this story.