(Lucca, 29 September 1780 – ibid., 27 May 1861). He was born into a rich, noble family, the son of Giovan Battista Mansi and Maria Caterina Massoni. His father died when he was young and in 1800 he was adopted by the aristocrat Francesco Mazzarosa, a relative, who made him his heir and whose name he took. In 1801, he married Marianna Orsucci, from a noble family, and from then devoted himself to the family and the management of his extensive property, though this did not prevent him from taking on numerous public duties in the administration of the Duchy of Lucca in collaboration with Carlo Ludovico of Bourbon. In 1825 he was minister of Public Education and in 1835 a member of the Council of State, of which he became president; he left this office in 1847, when as a prudent reformer, he favoured granting of the Constitution, establishment of the National Guard and freedom of the press and consequently came into conflict with the Duke of Lucca. Following renunciation and assignment of the small duchy to Leopoldo II of Tuscany, he worked with the Grand Duke, while also maintaining a position somewhat apart. Following Italian unification, he was elected senator in the Kingdom, but died a few weeks after the announcement.
He promoted educational, urban political and agricultural reform. He was in favour of the establishment of the local Savings Bank and construction of the Lucca-Pisa railway. As the author of numerous works on history, economics, law, religion and the arts, he was always cautiously open to new ideas and maintained a constant association with the fate of his native region.