Power was born in San Juan, Puerto Rico to Joaquín Power y Morgan, a Spaniard from the Basque Country (of Irish and French descent) who came to Puerto Rico in connection with the Compañía de Asiento de Negros, which regulated the slave trade in the island, and María Josefa Giralt y Santaella, a Catalan from Barcelona.

In 1795, the Peace of Basel resulted in Spain ceding Santo Domingo to France, but the French did not take possession of the colony.

Six years later in 1801, General Toussaint Louverture, a Black commander who was the de facto ruler of the neighboring French colony of Saint-Domingue, occupied Santo Domingo.

Colonel Rafael Conti, a fellow Puerto Rican, organized an expedition to restore Spanish rule in Santo Domingo.

The Junta Suprema dissolved itself before Power could arrive, nevertheless, the following year on April 16, he was again elected to represent Puerto Rico, this time in the Cortes of Cádiz, the parliamentary assembly serving as a Regency while awaiting Ferdinand VII's return, that had been convened by the Junta and was gathering in the Southern Spanish port of Cádiz.

One of his greatest supporters was Bishop Juan Alejo de Arizmendi, who during the official farewell Mass, gave Power his episcopal ring as a reminder that he should never forget his countrymen.

After arriving in Cádiz on June 8, 1810, he joined the growing number of delegates, which finally reached a quorum in September.

[8] On September 25, 1810, the second day of regular meetings, he was elected as vice-president of the Cortes and succeeded in obtaining powers which would benefit the economy of the Puerto Rico.

It also called for the establishment of a Sociedad Económica de Amigos del País en Puerto Rico on the island, which was approved in 1814.