Castillo was born on October 17, 1778, in Ujarrás, near Cartago, the colonial capital of the Provincia de Costa Rica [es], part of New Spain.

After being distinguished for his intelligence and spotless record, Castillo presented brilliant exam results, obtained a baccalaureate and was ordained a Catholic priest in 1802.

Castillo returned to Costa Rica preceded by the fame that his accomplishments had gained him in Nicaragua, and in 1806 he was named pastor of the incipient town of Villahermosa (later Alajuela; but aspiring to a higher destination, he returned in 1808 to León, entering the Tridentine University where he gained the post of professor of philosophy, which had been one of his most gifted disciplines, and later the more important charges of synodal examiner, prosecutor and vice-rector.

These rapid promotions, combined with the prestige won during his short return to Costa Rica, meant that when it came time to select a deputy for the Province of Costa Rica to the Cortes of Cádiz in Spain, convened for the salvation of Spain's independence--which was threatened by the formidable power of Napoleon who invaded the nation--his name was included, along with that of Friar José Antonio Taboada y José María Zamora.

In 1971, his remains were returned to Costa Rica, where they were interred in a mausoleum built in the central park of the town of Paraíso, near his birthplace of Ujarrás.