Joseph Fesch was born at Ajaccio in Corsica. His father Frantz, a Swiss officer in the service of the Genoese Republic, had married Angela Pietrasanta, the mother of Laetitia Bonaparte, after the death of her first husband. Joseph therefore is the uncle to the young Napoleon, and after the 1791 death of Luciano Buonaparte, archdeacon of Ajaccio, he became for a time the protector and patron of the family.
In 1789, when the French Revolution broke out, he was archdeacon of Ajaccio, and, like the majority of the Corsicans, he felt repugnance for many of the acts of the French government during that period; in particular he protested against the application to Corsica of the act known as the Civil Constitution of the Clergy (July 1790). As provost of the "chapter" in that city he directly felt the pressure of events; for on the suppression of religious orders and corporations, he was constrained to retire into private life.
Thereafter he shared the fortunes of the Napoleon Bonaparte family in the intrigues and strifes which ensued. Drawn gradually into espousing the French cause against Pasquale Paoli and the Anglophiles, he was forced to leave Corsica and to proceed with Laetitia and her son to Toulon, in early autumn, 1793. Failing to find clerical duties at that time (the Reign of Terror), he took several posts in civil life, until on the appointment of Napoleon Bonaparte to the command of the French "Army of Italy" he became a commissary attached to that army. This part of his career is obscure, but his fortunes rose rapidly when Napoleon became First Consul, after the coup d'état of 18 Brumaire (November 1799). When the restoration of the Roman Catholic religion was in the mind of the First Consul, Fesch resumed his clerical vocation and took an active part in the complex negotiations which led to the signing of the Concordat with the Holy See on July 15, 1801. His reward came in being made Archbishop of Lyon in August 1802. Six months later he received a further reward for his past services, being raised to the dignity of cardinal.
Appointed by Napoleon 4 April 1803 to succeed Cacault on the latter's retirement from the position of French ambassador at Rome, Joseph Fesch was assisted by Châteaubriand, but soon sharply differed with him on many questions. Towards the close of 1804, Napoleon entrusted to him the difficult task of securing the presence of Pope Pius VII at the forthcoming coronation of the emperor at Notre Dame, Paris (December 2, 1804). His tact in overcoming the reluctance of the pope (it was only eight months after the execution of the duc d'Enghien) received further recognition. He received the grand cordon of the Legion d'Honneur, became grand-almoner of the empire and had a seat in the French senate.
Subsequent events damaged his prospects. In the course of the years 1806-1807 Napoleon came into sharp collision with the pope on various matters both political and religious. Joseph sought in vain to reconcile them. Napoleon was inexorable in his demands, and Pius VII refused to give way where the discipline and vital interests of the church seemed to be threatened.
The disasters of the years 1812-1813 brought Napoleon to treat Pius VII with more lenity and the position of Joseph Fesch thus became for a time less difficult. On the first abdication of Napoleon (April 11, 1814) and the restoration of the Bourbons, he, however, retired to Rome where he received a welcome. The events of the Hundred Days (March-June, 1815) brought him back to France; he resumed his archiepiscopal duties at Lyon and was further named a member of the senate. On the second abdication of the emperor (June 22, 1815) Joseph Fesch retired to Rome, where he spent the rest of his days in dignified ease, surrounded by numerous masterpieces of art, many of which he bequeathed to the cities of Lyon and Ajaccio.
He died at Rome in 1839.