Annibale della Genga became pope on 28th September 1823 and his name became Leo XII. He was born in Genga in 1760 into a noble family.  He studied in Osimo (Campana College) from 1773 to 1778 and later in Rome, both at the Picene College and at the Pontifical Academy of Noble Ecclesiastics.  He had a brilliant ecclesiastical and diplomatic career, as he was secret waiter and canon of St. Peter, Archbishop of Tyre, apostolic nuncio in Cologne and in Munich, the nuncio extraordinary in France after the fall of Napoleon, cardinal and bishop of Senigallia, Prefect of the Congregation for Ecclesiastical Immunity and the cardinal vicar of Rome. In the conclave of 1823 the support of the faction of the zealous cardinals allowed him to be elected despite the strong opposition of the reformists supported by Austria.

Among the milestones reached during his pontificate, there are the courageous proclamation of the Jubilee in 1825, the effort to reorganize a centralized state, the fight against banditry. During his pontificate agreements were reached with the United States, the Netherlands and the former Spanish colonies of South America. A strong, determined and intransigent man, he was particularly inflexible towards the secret society of the Carbonari. He prohibited Bible societies, of Protestant mold and often financed by Freemasonry and, strongly influenced by the Jesuits, he reorganized the entire school system. He had a deep bond to his native town, where he ordered the building of the Public House, which at present temporarily houses the Museum of Genga. Here, besides masterpieces of the Italian Renaissance, two rooms are dedicated to the Pope: in a  room there are sacred items and vestments of the pope and in another room the works that he commissioned in his native land, such as the impressive neoclassical temple of the Madonna di Frasassi built in the gorge of Frasassi and the statue of the Madonna with Child attributed to the school of Antonio Canova, once placed within the same sanctuary. He also made improvements in the street between Genga and Fabriano. 

In spite of his age and poor health, he was pope for five short but intense years. He died on 10th February 1829.