He was young nobleman who exercised a position in the Royal court of Portugal, 14th Lord of Murça and Castro Daire, squire of Figueira, commander of Santa Maria de Freixas in the Order of Christ and honorary member of the Royal Academy of Sciences, in addition to holding several political offices, including that of governor and captain-general of Angola, minister and peer of the realm, appointed to a commission, by King John VI of Portugal, to draft a constitution for Portugal, minister and peer of the realm.

He also preoccupied himself with education in Angola and to issues of Catholic missionaries, where he solicited the closing of the Junta of Missions, noting that this institution did not function and was unnecessary.

The Informaçam, a manuscript of nine pages, revealed an acute sense of observation and developed a critical spirit and placed him in the echelon of the Portuguese literary experts.

On Junot's invasion, Miguel severed ties with the continent, now in the possession of the French forces; he ignored orders from Lisbon, supported by the exiled Royal family.

When Junot's forces were expelled, the English liberators entered the picture, functioning with Vice-Regal authority, maintaining a duality between the power in Lisbon and that in Rio de Janeiro, making the Captains-General dependent functionaries of the state.