During his papacy he effected the reconciliation of Henry IV of France to the Catholic faith and was instrumental in setting up an alliance of Christian nations to oppose the Ottoman Empire in the so-called Long War.

He was from a Florentine family, son of Silvestro Aldobrandini and Lesa Deti, and followed his father as a canon lawyer, becoming an Auditor (judge) of the Roman Rota, the highest ecclesiastical court constituted by the Holy See.

Aldobrandini won the gratitude of the Habsburgs by his successful diplomatic efforts in Poland to obtain the release of the imprisoned Archduke Maximilian, the defeated candidate for the Polish throne.

[6] After the death of Pope Innocent IX (1591), another stormy conclave ensued, in which a determined minority of Italian Cardinals were unwilling to be dictated to by Philip II of Spain.

Known to be very intelligent, disciplined, and in tune with the inner workings of the Church,[7] Cardinal Aldobrandini was elected on 30 January 1592, as a portent of more balanced and liberal Papal policy in European affairs.

[8] It was issued with the Bull Cum Sacrorum (9 November 1592)[9] which asserted that every subsequent edition must be assimilated to this one, that no word of the text could be changed, and that not even variant readings could be printed in the margin.

[13] In 1597, he established the Congregatio de Auxiliis which was to settle the theological controversy between the Dominican Order and the Jesuits concerning the respective role of efficacious grace and free will.

Notable cardinals named during his reign included Camillo Borghese (his successor Pope Paul V) as well as the noted theologians Robert Bellarmine and Caesar Baronius.

[6] Henry IV's friendship was of essential importance to the papacy two years later, when Alfonso II d'Este, Duke of Ferrara, died childless (27 October 1597), and the pope resolved to attach the stronghold of the Este family to the states of the Church.

These included most famously Troio Savelli, scion of a powerful ancient Roman family, and the youthful and noble Beatrice Cenci, who had murdered her father – probably as a consequence of his repeated abuses.

Pope Clement VIII participated personally in the final phases of the trial, inviting the Cardinals in charge of the case to proceed with the verdict.

In 1593, the bull Caeca et Obdurata reiterated Pope Pius V's decree of 1569, which banned Jews from living in the Papal States outside the cities of Rome, Ancona, and Avignon.

[14] The bull also alleged that Jews in the Papal States had engaged in usury and exploited the hospitality of Clement VIII's predecessors "who, in order to lead them from their darkness to knowledge of the true faith, deemed it opportune to use the clemency of Christian piety towards them" (alluding to Christiana pietas).

Clement was buried in St. Peter's Basilica, and later Pope Paul V (1605–21) had a mausoleum built for him in the Borghese Chapel of Santa Maria Maggiore, where his remains were transferred in 1646.