The April 1555 papal conclave was convoked after the death of Pope Julius III. Cardinals at the conclave generally grouped themselves into three major factions, according to their alignment with the French House of Valois, the Hapsburgs, or Italian states that remained independent of both major Catholic powers. After preparing a conclave capitulation that compelled whichever cardinal was elected pope to maintain neutrality in European wars, cardinals from the Holy Roman Empire joined in supporting the French faction's candidate, Cardinal Marcello Cervini. Cervini was elected Julius's successor, and chose to maintain his baptismal (birth) name as his papal name, becoming consecrated as Marcellus II.

The May 1555 papal conclave was convened on the death of Pope Marcellus II and elected Pope Paul IV as his successor.