He was ordained a priest, assisted the archbishop of Caesarea (now southeastern Turkey), and ultimately became archbishop himself, in spite of opposition from some of his suffragan bishops, probably because they foresaw coming reforms.
One of the most damaging heresies in the history of the Church, Arianism, which denied the divinity of Christ, was at its height. Emperor Valens persecuted orthodox believers, and put great pressure on Basil to remain silent and admit the heretics to communion. Basil remained firm, and Valens backed down. But trouble remained. When the great St. Athanasius died, the mantle of defender of the faith against Arianism fell upon Basil. He strove mightily to unite and rally his fellow Catholics who were crushed by tyranny and torn by internal dissension. He was misunderstood, misrepresented, accused of heresy and ambition. Even appeals to the pope brought no response. For my sins I seem to be unsuccessful in everything.
He was tireless in pastoral care. He preached twice a day to huge crowds, built a hospital that was called a wonder of the world (as a youth he had organized famine relief and worked in a soup kitchen himself) and fought the prostitution business.
Basil was best known as an orator. His writings, though not recognized greatly in his lifetime, rightly place him among the great teachers of the Church. Seventy-two years after his death, the Council of Chalcedon described him as the great Basil, minister of grace who has expounded the truth to the whole earth.