Giacomo Antonelli, an Italian cardinal and statesman, born at Sonnino, near Terracina, April 2, 1806. He was educated at the great seminary of Rome, and having early distinguished himself by his ability, he was raised to the prelacy, after taking orders, and appointed by Gregory XVI. to various civil offices, attaining in 1845 to the post of minister of finance. After the accession of Pius IX. he was made cardinal (June 12, 1847), and in 1848 prime minister, in which position he won at first the favor of the popular party. Though continuing to be the pope's chief political adviser, the opponents of innovations soon compelled him to make place for Mamiani. After the assassination of the latter's successor, Rossi, Antonelli urged Pius IX. to leave Rome, and joined him at Gaeta (November, 1848), where he conducted the negotiations which resulted in the pope's return to his capital (April 12, 1850) under the protection of the French army of occupation. Antonelli was now made secretary of foreign affairs, in which capacity his retrogressive policy exasperated the liberals, and even led to remonstrances on the part of foreign powers, but without shaking his position.

He protested in vain against the progress of events in Italy, reorganized the civil administration on the most reactionary basis, and was opposed in his absolute policy even by some of his colleagues in the papal government, the principal of whom, Mgr. de Merode, minister of war. was removed in 1805. In 1807 he was made curator ad interim of the university of Rome. In January, 1868, by the death of Cardinal Ugolino, he became dean of the order of cardinal deacons. After the evacuation of Rome by the French in August, 1870, he appealed to various foreign powers for assistance, and remonstrated against the success of Victor Emanuel, who made his formal entry into Rome Nov. 21, 1871. An attempt upon his life was made in 1855.