As a man, Vieira would have made a nobler figure if he had not been so great an egotist and so clever a courtier, and the readiness with which he sustained directly opposite opinions at short intervals with equal warmth argues a certain lack of sincerity.
The ill-fated Vieira de Castro excited the greatest admiration by his impassioned speeches in the Chamber of Deputies during the 'sixties; the nearest modern counterpart to these distinguished men is the orator Antonio Candido Ribeiro da Costa.
Ultimately Vieira returned to Portugal with a papal bull exempting him from the jurisdiction of the grand inquisitor, and in January 1681 he embarked for Brazil.
In 1647 Vieira began his career as a diplomat, in the course of which he visited England, France, Holland and Italy.
Carel, Vieira, sa vie et ses oeuvres (Paris, 1879); Luiz Cabral, Vieira, biog., caractere, eloquence (Paris, 1900); idem, Vieira pregador (2 vols., Oporto, 1901); Sotero dos Reis, Curso de litteratura Portugueza e Brazileira, iii.
On the throne of Portugal, Brazil gave him its allegiance, and Vieira was chosen to accompany the viceroy's son to Lisbon to congratulate the new king.