He studied law in the University of Oviedo, where he became interested in politics and approached the Moderate Party.

In the regency of Queen Maria Christina of the Two Sicilies (1833–1840), Mon was appointed for his first high political office, minister of finance from 1837 to 1838, in a moderate cabinet headed by Narciso Fernández de Heredia, 2nd Count of Heredia-Spínola.

After the downfall of the moderates, the unionist Leopoldo O'Donnell, 1st Duke of Tetuan, offered him several ministerial portfolios, which he always declined.

Mon preferred to be in posts away from the first line of political life, such as ambassador to the Holy See or to France.

Mon lived long enough to see the reign of Amadeo I of Spain, the First Spanish Republic and finally the Restoration of King Alfonso XII, which he supported as a personal friend of Antonio Cánovas del Castillo.