Following the example of Cuba, this militia was first established in December 1864 in order to fill the void left by the units of the local garrison sent to the war in Santo Domingo (1863–1865).

After a few first years of barely any activity, several Volunteer units were created across the island as a result of the Grito de Lares, the incipient first outcry for independence in Puerto Rico of September 23, 1868.

This party was opened to all Spaniards, both Creoles and peninsulares (from mainland Spain), but the latter played a prominent role providing many of its leaders and ranks.

Many in the island's elite joined the Volunteers as a symbol of social status and loyalty to Spain (e.g., Manuel Egozcue Cintrón, Rafael Janer y Soler, Francisco J. Marxuach, Pompeyo Oliu y Marxuach, Narciso Vall-Llovera Feliu, etc.).

The Corps's conduct during the war was negatively affected by the distrust showed towards them by many Army officers and the order issued by the Governor having them concentrating in the biggest towns, leaving their homes and families unprottected.

Other—though perhaps less quantifiable—factors contributing to Volunteer inaction were the signal winds of change sweeping over the remnants of Spain's once vast imperial possessions; the Cortes's belated attempts at establishing an autonomist insular government in 1897; and the U.S.'s undisguised expansionist aims, combined with the contagion of assimilationist and insurrectionist groups operating from within the island and outwards from the U.S.[2] Additionally, by the time of the US invasion of the island on July 25, 1898, the Voluntarios and indeed most everyone else in Puerto Rico, was well aware that the city of Santiago de Cuba had capitulated and that Admiral Montijo's fleet in the Philippines had been virtually destroyed.