He was born in Delft, the son of Manuel of Portugal and Countess Emilia of Nassau, who was a daughter of William the Silent.

[1] Already in 1613, his uncle, the Stadtholder Maurice of Orange, promoted him as captain, because of the income associated with this position and not with the aim to take over a military command.

Manuel António started a military career as Rittmeister in service of Spain and at the archducal court.

[4] Shortly thereafter he was captured near Geldern by Cardinal-Infante Ferdinand of Austria and General Guillaume de Lamboy, taken to Brussels and — on his request — transferred to "his" monastery.

This relation produced the following offspring: The sources point out that the countess — who descended from an impoverished branch of her family, which had been buffeted by the Thirty Years' War — brought little to the marriage.