He was the son of Pedro Vélez de Guevara and María de Tassis. He married Catalina Vélez, 5th Countess of Oñate.[4] When her only brother Ladrón was killed in battle on sea against the English in 1588, Catalina became Countess of Oñate. After the death of his cousin
Juan de Tassis y Peralta, 2nd Count of Villamediana he also the title of Count of Villamediana.[5]
During the
Thirty Years' War, the Spanish sent an army from
Brussels under
Ambrosio Spinola to support the Emperor, and, as the Spanish ambassador in Vienna, don Íñigo persuaded Protestant
Saxony to intervene against Bohemia in exchange for control over
Lusatia. The Saxons invaded, and the Spanish army in the West prevented the Protestant Union's forces from assisting.
In Spain he had ambitions to follow the
Duke of Lerma as valido, but the King's
favourite and Íñigo's adversary was chosen, the
Count-Duke of Olivares. He lost the King's favor and
Luis de Haro became the successor of Olivares.
Children
Pedro, 6th Count of Oñate, killed in Milan after falling off his horse