He received his education from the Jesuits at Rimini and the Piarists of Urbino, and in 1724, at the age of nineteen, entered the Order of Friars Minor Conventual of St. Francis with the Franciscan name of Lorenzo Francesco. In 1741 he was made definitor generalis of the order (Catholic Encyclopedia). Ganganelli became a friend of Pope Benedict XIV (1740–58). In 1758 he was appointed by that Pope to investigate the issue of the traditional blood libel regarding the jews, which he found to be untrue Pope Clement XIII (1758–69) appointed him a cardinal in 1759, at the insistence of Lorenzo Ricci, the General of the Jesuits.
Ganganelli was elected Pope Clement XIV on May 19 1769 and was installed on June 4, 1769, after a conclave that had been sitting since 15 February, 1769, heavily influenced by the political manoeuvres of the ambassadors of Catholic sovereigns who were opposed to the Jesuits. Some of the pressure was subtle: for an unprecedented impromptu visit to the conclave by Emperor Joseph II (1765–90) and his brother the Grand Duke of Tuscany, officially incognito, the seals were broken, the Austrians inspected the proceedings with great interest and brought with them a festive banquet (Pirie 1965 p 269). During the previous pontificate the Jesuits had been expelled from Portugal and from all the Bourbon courts: France, Spain, Naples, and Parma; now the general suppression of the order was urged by the faction called the "court cardinals", who were opposed by the diminished pro-Jesuit faction, the Zelanti ("zealous"), who were generally opposed to the encroaching secularism of the Enlightenment.
King Louis XV's (1715–74) minister, the duc de Choiseul, had former experience of Rome as French ambassador, and was Europe's most skilled diplomat. "When one has a favour to ask of a Pope", he wrote, "and one is determined to obtain it, one must ask for two." Choiseul's suggestion, advanced to the other ambassadors, was that they should press, in addition to the Jesuit issue, territorial claims upon the Patrimony of Peter: the cession of Avignon and the Comtat Venaissin to France; to Spain the duchies of Benevento and Pontecorvo; for Naples an extension of territory adjoining the Papal States; and for Austria an immediate and final settlement of the vexed question of Parma and Piacenza that had occasioned a diplomatic rift with Pope Clement XIII.
Clement XIV's policies were calculated from the outset to smooth the breaches with the Catholic Crowns that had developed during the previous pontificate. The dispute between the temporal and the spiritual Catholic authorities was perceived as a threat by Church authority, and Clement XIV worked towards the reconciliation of the European sovereigns. The arguing and fighting among the monarchs seemed poised to lead Europe towards heavy international competition – a situation which would have resembled the European situation in the late nineteenth century.
By yielding the Papal claims to Parma, Clement XIV obtained the restitution of Avignon and Benevento, and in general he succeeded in placing the relations of the spiritual and the temporal authorities on a friendlier footing. The Pope went on to engage in the suppression of the Jesuits, the decree to this effect being written in November 1772, and signed in July 1773.
This measure, to late nineteenth century Catholics, had covered Clement XIV's memory with infamy in his church, and was also quite controversial, with the Catholic Encyclopedia (?) supporting Clement XIV's suppression of the Jesuits as "abundantly justified".
His work was hardly accomplished, before Clement XIV, whose usual constitution was quite vigorous, fell into a languishing sickness, generally attributed to poison. No conclusive evidence of poisoning was ever produced. The claims that the Pope was poisoned were denied by those closest to him, and as the Annual Register for 1774 stated, he was over 70 and had been in ill health for some time.
Jacques Cretineau-Joly, however, wrote a critical history of the Pope's administration.