Joseph Fesch was a cardinal, diplomat, Catholic archbishop and French art collector of Corsican origin; he was the uterine brother of Letizia Ramolino, mother of Napoleon Bonaparte.
He was born in Ajaccio January 3, 1763 by Octave Fesch, a Swiss who had converted from Protestantism to Catholicism on the occasion of the marriage, and by Angela Maria Pietrasanta, former widow of Giovanni Gironimo (or Gian Girolamo) Ramolino and mother of a child, Letizia Ramolino, the future mother of Napoleon.
Joseph was sent to the priesthood before the French Revolution: he studied in the seminary of Aix-en-Provence, was ordained a presbyter in 1785 and soon returned to Corsica. With the outbreak of the French revolution he changed his life prospects: in 1790 he swore the civil constitution of the clergy, later he threw the cassock and in 1796 became commissioner of the French army, led by his nephew, in the First Italian campaign.
He obtained to return to the Catholic Church after Napoleon signed the Concordat of 1801 with Pius VII. On 29 July 1802 he was appointed archbishop of Lyon and a few months later, in the consistory of 17 January 1803, he was elevated to the rank of cardinal of San Lorenzo in Lucina. In 1803 he was appointed French ambassador to Rome, having François-René de Chateaubriand as secretary of the embassy; he succeeded in obtaining the trust of Pius VII so much so that in 1804 he accompanied him to France, together with card. Borgia for the coronation of Napoleon.

He became, by the influence of his nephew, Grand Chaplain of the French Empire and was appointed by the same Knight of the Grand Cross of the Legion of Honor as well as French Count and Senator. Charles IV, King of Spain, made him a Knight of the Golden Fleece.
In the following years Napoleon's ecclesiastical politics proceeded towards the clash with the Catholic Church. The refusal of Pius VII to ordain bishops only the candidates chosen by Napoleon prompted the latter, on the advice of some French theologians, to hold a national council, which opened on June 17, 1811. Although Fesch felt very strong family ties , however, he sided with the pope against his nephew emperor: Napoleon took away all the benefits he had given him, and Fesch retired to Lyons, devoting himself to the care of the diocese. The star of Napoleon I had been turned down forever in 1814. He was exiled to Rome and thanks to the magnanimity of Pope Pius VII took up residence at Palazzo Falconieri in Via Giulia, and remained there until his death, taking an interest in art. He was in fact a passionate collector of Napoleonic paintings and papers; but not only, because he remembers him in the documents of the time, who was a generous benefactor of orphans, of illegitimate children, of very poor girls to whom he donated the wedding dress and sometimes left some small dowry.
He was buried from 1839 to 1859 in the church of the Sisters of the Santissima Croce in Corneto (Civitavecchia), since 1859 he is buried, together with his maternal sister Letizia Ramolino and the husband of this Carlo Buonaparte, in the crypt of the imperial chapel of Ajaccio built by Luigi Napoleone future Emperor of the French with the name of Napoleon III.
In the building he had built in his native Ajaccio as "Institut des Arts et des Sciences", after his death, part of the collection of about 16,000 paintings that the cardinal had collected in Rome were transferred, and his legacy to the city, consisting of about a thousand pieces between paintings, furniture and liturgical furnishings. This was the original fund on which the Fesch Museum was established in the late 1850s.