Italian pope from 1775 to 1799, whose tragic pontificate was the longest of the 18th century.

He held various papal administrative positions before being ordained priest in 1758. Progressing rapidly, he became treasurer of the apostolic chamber under Pope Clement XIII in 1766, and in 1773 was made cardinal by Pope Clement XIV, after whose death a four-month conclave elected Braschi on Feb. 15, 1775.

The church needed spiritual and institutional reform, and the papacy was nearly stripped of power and influence. The religious orders, the essential medium of papal influence in the church, were under attack by the protagonists of the Enlightenment; and the royal leaders of Catholic Europe, the pope's traditional allies, were now indifferent to papal interests, being concerned only with the possibilities of using the national churches in their schemes for administrative reform.

In October 1781 the Holy Roman emperor Joseph II inaugurated his reforming Edict of Toleration, whereby non-Catholic minorities received considerable religious toleration, “unnecessary” monasteries were dissolved, diocesan boundaries were redrawn, and seminaries were placed under state control. Further detailed reforms were intended to abolish such practices as festivals and superstitious reverences that were not considered in keeping with the Enlightenment. Pius intervened in 1782 by personally visiting Vienna but failed to secure any concessions. Joseph's application of Febronianism, an ecclesiastical doctrine that advocated restriction of papal power, subsequently became known as Josephinism. Meanwhile, the church in the Habsburg dominions remained wealthy and influential but subordinate to the state.

The French issue was equally overwhelming. Preliminaries to the Revolution were occurring, and the new government turned to the church's wealth, which it confiscated as a direct backing for its currency. Under the Civil Constitution of the Clergy (1790), France intended to force a reform of the French Church, thus causing a major conflict between Rome and the Revolution, whose scheme resembled Joseph's designs. Pius took no immediate action, but when an oath of fidelity to the new regime was demanded from the clergy, he formally denounced the Civil Constitution and the Revolution on March 10, 1791. The French Church was completely split.

Pius was on good terms with the allies against France in 1793 and felt that he could rely on them, but in 1796 his territory was invaded after the last Austrian defeat by Napoleon (Napoleon I), who forced the Pope to sign a peace treaty at Tolentino on Feb. 19, 1797. In the following December, a riot in Rome led to French occupation of that city on Feb. 15, 1798, and the proclamation of a republic by a group of Italian patriots. Aged and frail, he was seized by the French in March 1799 and died a prisoner in France the following August.