The parents were Franz Joseph Feschs Faesch (1723-1775), captain of a standing in the service of the Republic of Genoa Swiss regiment, and Angela Maria Pietrasanta (1725-1790), which he had married in 1757. Angela Mary was the widow of the Corsican Giovanni Geronimo Ramolino and brought out of this marriage, the seven year old daughter Laetitia Ramolino into the marriage, the mother Napoleon Bonaparte should be later. Thus Joseph Fesch was a step-uncle of the later French Emperor.
Fesch embarked on a clerical career. Like the majority of Corsicans, he rejected the actions of the French Revolution and protested in July 1790 especially against the introduction of the French Civil Constitution of the Clergy in Corsica. 1791, after the death of Luciano Bonaparte, he followed after this both as Archdeacon of Ajaccio as well as patron of the Bonaparte family, but had to after the abolition of religious orders to retire into private life.
Fesch found himself in contrast to Pascal Paoli's pro- British policies and was forced to leave with his stepsister Corsica. In southern France they joined Napoleon Bonaparte and came with him in the fall of 1793 to Toulon. Since Fesch could not find a spiritual items - it was the time of the Great Terror - he held various positions in the administration, including at Montesquiou army in Savoy. In 1796 he received the first Italian campaign of his nephew Bonaparte an appointment as Commissar for War, but had to due to many lawsuits against him that have become loud that he looted, including paintings have robbed resign this office again soon.
The coming to power of Napoleon in November 1799 led to an increase his prospects. After the Concordat with Pope Pius VII in 1801 Fesch returned to spiritual activities back - Jacques -André Emery gave his return to full communion with Rome - was Domkanonikus to Bastia, in April 1802 Archbishop of Lyon and in 1803 Cardinal and French envoy at the papal yard. In 1804 he accompanied the Pope to the coronation of Napoleon I in Paris, took place on the eve of the coronation of Napoleon and Joséphine's church wedding, was Grand Almoner of the Empire, Count and Senator and 1806 chosen by Prince Primate Dalberg coadjutor and successor. He presided in 1810 at Paris, a council of the French clergy and spoke on the same so decided for the Pope and against its treatment by Napoleon in that he now had to live to Lyon in a kind of exile.
At the approach of the Austrians (1814 ), he fled with his sister Laetitia, the mother of the Emperor, to Rome, peer of France, after Napoleon's return, but returned after the battle of Waterloo to Rome and lived in complete seclusion the arts and Sciences. The request of the French government to renounce his archbishopric Lyon, he firmly rejected, even though he in fact his office is not exercised.
He died on 13 May 1839. His world-famous collection of paintings to have numbered more than 20,000 images, was gradually auctioned after his death and the proceeds used for family Scholarships.