Carlo Borromeo, whose family had intended him from childhood for a career in the church, had held many important offices in Rome while his late uncle, Giovanni Angelo de'Medici, reigned as Pope Pius IV.

Upon the death of his uncle, Borromeo takes part in the conclave that on January 7, 1566, elects Dominican Cardinal Ghislieri, a member of the Roman Inquisition.

Born into a poor family at Bosco Marengo, Antonio (also called Michele) Ghislieri, had held a series of important offices in the Dominican order.

Attracting the favor of Pope Paul IV for the austerity of his life and his zeal for orthodoxy, he had in 1557 been made a cardinal.

Ghislieri is crowned Pope Pius V on January 17, his sixty-second birthday.