He started his military career in the Spanish Army in Peru having been appointed colonel of the Regiment of Infantry of Caraz when he was fifteen years old.

Once the Prince of Asturias married Princess Maria Antonia of Naples, a party called Napolitan was formed in the court decisively active against Godoy.

That same year, Charles IV appointed San Carlos Mayordomo Mayor of the king, the highest position in court, in an effort to get closer to his son.

He drafted and negotiated the Treaty of Valençay with France, which recognized Ferdinand VII as legitimate king of Spain and the restitution of the occupied territories.

He married twice : first with María del Rosario de Silva, Countess of Fuenclara, Duchess of Arenberg, First Class Grandee of Spain, from whose marriage he had no children.

After her death in 1802, he married the next year María Eulalia de Queralt y Silva (1787-1863), daughter of the Counts of Santa Coloma, Grandee of Spain and niece of his previous wife.