He was the eldest son of the Galician knight Garcia Sarmiento de Soutomaior —Lord of Salvaterra de Miño, who served as "corregidor" of Toro and governor of the Canary Islands— and of Juana de Acuña, heiress of the noble house of Acuña. He was born in Astorga, near Galicia, inheriting large estates both in Galicia and in Old Castile. He took an active part during the Anglo-Spanish War in repelling an English raid led by Sir Francis Drake on Baiona and Vigo in 1585. They met forces again four years later in Vigo, after the "English Armada" was turned away in A Coruña and Lisbon; there Drake was rejected but not before the bombing and sack of the town. As a result of these military successes, he was appointed by King Philip II of Spain as governor of Baiona, and keeper of the fortress of Monte Real, so warding the southern frontier and sea coast of Galicia. Later, in 1596, he was appointed first "corregidor" of Toro, and later of Valladolid, then the residence and capital of King Philip III. From that moment he was forced to reconcile both roles, as courtier and corregidor in the capital, and as soldier and Capitan in Galicia: in 1603 he was sent from court to Vigo to superintend the distribution of the treasure brought from America by two galleons which were driven to take refuge there; on his return he was appointed a member of the board of finance. In 1609 he repelled a Dutch naval attack on the coast of Galicia.