His election as pope occurred at a conclave held at Perugia that lasted four months while cardinals argued over whether to call in Charles I of Anjou, the youngest brother of Louis IX of France, to carry on the papal war against the Hohenstaufens.

[4] In this period, the See of Rome was engaged in a conflict with Manfred, King of Sicily, the illegitimate son and designated heir of Holy Roman Emperor Frederick II of Hohenstaufen, but whom papal loyalists, the Guelfs, called "the usurper of Naples".

He immediately took steps to ally himself with Charles of Anjou, his erstwhile patron's brother and the impecunious French claimant to the Neapolitan throne.

Charles was willing to recognize the Pope as his feudal overlord (a bone of contention with the Hohenstaufens) and was crowned by cardinals in Rome, where Clement IV, permanently established at Viterbo, dared not venture, since the anti-papal Ghibelline party was so firmly in control there.

Though Clement did not condemn to death at the stake those who harboured copies of it,[7] and, responding to a denunciation of the Talmud by Pablo Christiani,[8] he ordered that the Jews of the Crown of Aragon submit their books to Dominican censors for expurgation.

In 1266, after the Battle of Benevento, Pope Clement IV conceded for gratitude his coat of arms to the Guelph Party of Florence as official approval to their supremacy and therefore they could take power in many of the other northern Italian cities.

In 1267, Pope Clement IV and King James I of Aragon sent an ambassador to the Mongol ruler Abaqa in the person of Jayme Alaric de Perpignan.

[14] Within months Clement IV was dead as well, and was buried at the Dominican convent, Santa Maria in Gradi, just outside Viterbo, where he resided throughout his pontificate.