In 1647 Vieira began his career as a diplomat, in the course of which he visited England, France, the Netherlands and Italy. In his "Papel Forte" he urged the cession of Pernambuco to the Dutch as the price of peace, while his mission to Rome in 1650 was undertaken in the hope of arranging a marriage between the heir to the throne of Portugal and the only daughter of King Philip IV of Spain. His success, freedom of speech and reforming zeal had made him enemies on all sides, and only the intervention of the king prevented his expulsion from the Society of Jesus, so that prudence counselled his return to Brazil.