Following the events of the Revolution of April 19, 1810 where Montilla participated, the commanding General and other colonial officials designated by Joseph Bonaparte to oversee the Captaincy General of Venezuela, were deposed by an expanded municipal government in Caracas that called itself: the Supreme Junta to Preserve the Rights of Ferdinand VII (La Suprema Junta Conservadora de los Derechos de Fernando VII).
One of the first measures of revolutionaries was to send diplomatic missions abroad to seek support and recognition of the Supreme Junta of Caracas as the legitimate councilor of Venezuela in the absence of the King.
In 1814, following defeat by the royalists, he was forced to emigrate to Cartagena de Indias in the New Granada, where he undertook the defense of the city against the siege imposed by the Spanish general Pablo Morillo.
Bolivar employed the Legion as an amphibious raiding force supported by Luis Brion fleet, harassing royalist garrisons on the north coast of New Granada to distract enemy attention from his own inland campaign.
[2] Later in 1820 he landed in Sabanilla, in the province of Cartagena, opened the port for trade, defeated the royalists at Pueblo Nuevo and established communications with Bolivar's forces in the interior of New Granada.
[5] However, in January 1833, Congress allowed him to return, and in November 1833 Montilla was appointed minister plenipotentiary to restore friendly relations with England and France and to seek recognition of Venezuelan independence from Spain, a mission that was largely successful.