Charles III was born on January 20, 1716, in Madrid, the eldest son of King Philip V of Spain and his second wife, Elisabeth Farnese. Because Philip already had sons from his first marriage, Charles was initially expected to rule Italian territories claimed through his mother rather than inherit Spain. He received a princely education in religion, languages, history, military affairs, riding, and hunting.

Elisabeth Farnese energetically pursued thrones for her sons. At fifteen Charles became Duke of Parma and Piacenza. During the War of the Polish Succession, Spanish forces conquered Naples and Sicily, and in 1734 Charles became king of those realms. His early kingship gave him decades of direct governing experience before he inherited the Spanish crown. He married Maria Amalia of Saxony in 1738, and their household produced a secure succession.

In Naples, Charles promoted administrative reform, commerce, road building, archaeology, and major architectural projects. He attempted to limit some ecclesiastical privileges and strengthen royal authority while working through ministers experienced in Enlightenment statecraft. The discovery and excavation of Herculaneum and Pompeii began during his reign, contributing to European interest in antiquity.

Charles also learned the vulnerability of Mediterranean kingdoms to naval power. He sought to preserve independence from great-power conflicts but remained tied to the wider Bourbon dynasty. When his half-brother Ferdinand VI of Spain died without children in 1759, Charles inherited Spain and transferred Naples and Sicily to his son Ferdinand. He arrived in Madrid as a mature and experienced monarch. British maritime expansion and France’s wartime difficulties soon pressured him to reconsider Spanish neutrality and renew the Bourbon Family Compact.