Philip II began governing territories of the Spanish monarchy before succeeding to its principal crowns. His marriage to Mary I made him king consort of England from 1554 to 1558, but it produced no heir or permanent union. Through Charles V's abdications in 1555–1556, Philip inherited Spain, the Netherlands, Italian possessions, and expanding overseas dominions. Victory over France at Saint-Quentin and the Peace of Cateau-Cambrésis in 1559 helped establish his position as a major European ruler.

Philip returned to Spain, made Madrid the court's principal seat in 1561, and directed government through councils, written consultations,. He commissioned El Escorial as a monastery, palace, and dynastic monument. His monarchy drew resources from American silver and taxation, but recurrent debt crises forced suspensions of payments. The size and diversity of his territories made administration and communication difficult, and his religious commitment shaped policy without eliminating political bargaining.

In the Mediterranean, Philip's forces and allies confronted Ottoman power; the Holy League's victory at Lepanto in 1571 checked the Ottoman fleet without ending the rivalry. Within Spain, the Morisco revolt in the Alpujarras was suppressed, followed by forced dispersal of its population. In the Netherlands, resistance to taxation, centralization, and religious persecution developed into a prolonged revolt. Harsh repression under the Duke of Alba failed to restore lasting obedience, and the northern provinces eventually escaped Spanish rule. In 1580 Philip secured Portugal's crown through a dynastic claim backed by military force, adding its overseas empire to his monarchy.

Conflict with Elizabeth I's England combined religion, support for Dutch rebels, and attacks on Spanish commerce. The Armada of 1588 failed to achieve an invasion, although Spain continued to possess major military and naval resources. Philip also intervened in France's religious wars and supported Catholic opponents of Henry IV. He died in 1598 and was succeeded by Philip III. His career sustained a vast Catholic monarchy and extended its reach, but also exposed the costs of imperial commitments and coercive religious government. Later reputations as either a prudent ruler or a fanatical tyrant reflect conflicting perspectives; his record includes administrative effort, artistic patronage, fiscal strain, and warfare that placed severe burdens on subjects across several continents.