Born near Piacenza, probably at the village of Fiorenzuola, his father was a gardener, and he himself became first connected with the church in the humble position of verger in the cathedral of Piacenza. Having gained the favour of Bishop Barni he took priest's orders, and afterwards accompanied the son of his patron to Rome.
During the war of the Spanish succession Alberoni laid the foundation of his political success by the services he rendered to the duke of Vendôme, commander of the French forces in Italy; and when these forces were recalled in 1706 he accompanied the duke to Paris, where he was favourably received by Louis XIV.
In 1711 he followed Vendôme into Spain as his secretary. Two years later, the duke having died in the interval, Alberoni was appointed consular agent for Parma at the court of Philip V of Spain, being raised at the same time to the dignity of count. On his arrival at Madrid he found the princesse des Ursins all but omnipotent with the king, and for a time he judged it expedient to use her influence in carrying out his plans. In concert with her he arranged the king's marriage with Elizabeth Farnese of Parma.
The influence of the new queen being actively exerted on Alberoni's behalf, he speedily rose to high position. He was made a member of the king's council, bishop of Malaga, and in 1715 prime minister, and was raised to the dignity of cardinal in 1717. His internal policy was exceedingly vigorous. The main purpose he put before himself was to produce an economic revival in Spain by abolishing internal custom-houses, throwing open the trade of the Indies and reorganizing the finances.
With the resources thus gained he undertook to enable King Philip V to carry out an ambitious policy both in Italy and in France. The impatience of the king and his wife gave the minister no time to mature his plans. By provoking England, France, the Netherlands and the Empire at once it brought a flood of disaster on Spain for which Alberoni was held responsible. On December 5, 1719 he was ordered to leave Spain, Elizabeth herself having taken an active part in procuring the decree of banishment.
He went to Italy, and there had to take refuge among the Apennines, Pope Clement XI, who was his bitter enemy, having given strict orders for his arrest. On the death of Clement, Alberoni boldly appeared at the Conclave, and took part in the election of Innocent XIII (1721), after which he was for a short time imprisoned by the pontiff on the demand of Spain. At the next election (1724) he was himself proposed for the papal chair, and secured ten votes at the Conclave which elected Benedict XIII.
Benedict's successor, Clement XII (elected 1730), named him legate of Ravenna, in which capacity he incurred the pope's displeasure by the strong and unwarrantable measures he adopted to reduce the little republic of San Marino to subjection to Rome. He was consequently replaced by another legate in 1740, and soon after he retired to Piacenza.
Clement XII appointed him administrator of the hospital of San Lazzaro at Piacenza in 1730. The hospital was a medieval foundation for the benefit of lepers. The disease having disappeared from Italy, Alberoni obtained the consent of the pope to the suppression of the hospital, which had fallen into great disorder, and replaced it by a college for the education of seventy poor boys for the priesthood, under the name of the Collegio Alberoni, which it still bears.
He died leaving a sum of 600,000 ducats to endow the seminary he had founded, and the residue of the immense wealth he had acquired in Spain to his nephew. Alberoni left a large quantity of manuscripts; but the genuineness of the Political Testament, published in his name at Lausanne in 1753, has been questioned.