Ambrose was born into a Christian family. His father was a Prefect of Gaul and his mother a pious lady. Both his brother, Satyrus, and his sister, Marcellina, are canonized saints.
By the age of thirty-three, Ambrose was an accomplished lawyer, the Governor of Milan and owner of a large estate. Though confessedly of Christian persuasion, he was not as yet baptized.
In the last quarter of the fourth century, many heresies assailed the Church. Perhaps, one of the most virulent was that of Arianism, which denied the divinity of Christ. When the bishop of Milan, an Arian, died in 374, party strife broke out in the city. Some citizens demanded an Arian bishop be appointed to succeed him, others an orthodox Catholic one.
Walking into an angry assembly which had convened in a church, Governor Ambrose began to appeal that they settle things more peaceably. Suddenly a voice shouted, “Ambrose for bishop!” and the cry was taken up by the crowd.
Ambrose ran and hid in the house of a senator friend. The Emperor, however, insisted that the governor accept the responsibility and he ultimately submitted. Many expected him to rule as an Arian, but the same stubbornness with which he had resisted the ecclesiastical appointment, he now employed in serving the Truth.
He began by assiduously applying himself to the study of Holy Scriptures and theology, his knowledge of Greek greatly facilitating his studies.
Eventually, he who had begun as a jurist succeeded as a theologian. A great orator, he influenced the conversion of St. Augustine of Hippo, who was impressed with his erudition on sacred themes, and mentions the illustrious bishop in his Confessions.
Adopting a personal life of simplicity and hard work, Ambrose devoted himself entirely to the service of his flock. Throughout his episcopate he was loving and strong, protecting his flock against Arianism, paganism, and the demands of rulers who gave their allegiance to the Arian heresy. Several times he heroically refused to hand over the churches to the Arian Empress Justina, regent for her young son, Valentinian II. He prevailed every time.
Despite his differences with the empress, as a statesman, he was called twice to advocate the cause of Justina with Magnus Maximus, a former military man, who had usurped the power in Gaul and who wished to take the reins of government in Italy as well. The first time Ambrose prevailed, the second time Maximus went ahead with the take-over. When he invaded Milan, Ambrose melted Church gold plate to relieve the sufferers.
Theodosius I, Emperor of the East came to the aid of Italy, and regained power from Maximus. Though St. Ambrose confronted him severely on some issues, they had a good relationship.
Ambrose ruled not only with great administrative ability, but also ranks with Sts. Augustine, Jerome, and Gregory the Great as one of the greatest theologians and Doctors of the Church.
He died on 4 April 397 and his body is venerated in the Church of Sant’Ambrogio in his city of Milan.