After he (Ambrose) had been taught in the liberal disciplines...

…he left the city (Rome) and began his public career in the court of the praetorian prefect. So well did he plead his cases here that he was chosen by the illustrious Probus, then the praetorian prefect, to be his adviser. After this, he received consular rank so as to govern the province of Liguria and Aernilia. And then he came to Milan.

About the same time, after the death of Auxentius (October, 374), a bishop of the Arian heresy who retained possession of the church after Dionysius the Confessor, of blessed memory, was sent into exile, when the people were about to revolt in seeking a bishop, Ambrose had the task of putting down the revolt. So he went to the church. And when he was addressing the people, the voice of a child among the people is said to have called out suddenly: “Ambrose bishop.” At the sound of this voice, the mouths of all the people joined in the cry: “Ambrose bishop.” Thus, those who a while before were disagreeing most violently, because both the Arians and the Catholics wished the other side to be defeated and their own candidate to be consecrated bishop, suddenly agreed on this one with miraculous and unbelievable harmony.

And when he realized this, he left the church and had a tribunal prepared for himself indeed, he mounted higher steps because he would soon become a bishop. Then, contrary to his usual behavior, he ordered tortures to be inflicted on people. Although he did this, the people none the less kept shouting: “Your sin be upon us.”. … Then, in a disturbed state of mind, he returned home and wanted to declare himself a philosopher, but he was about to become a true philosopher of Christ, since, in despising the pomp of this world, he was about to follow the footsteps of the fisherman who brought people to Christ not by a show of words but by simple language and by the reasonableness of the true doctrine. For they, having been sent without wallet, without staff, converted even philosophers. But, when he was restrained from making this profession, he had “public women” come to him openly for this one purpose, that, when the people saw this, they would recall their intention. The fact was, however, the people kept crying out more and more: “Your sin be upon us.”

When he saw that nothing could accomplish his intention, he prepared his flight and left the city at midnight. Since he intended to make his way to Ticinum, he was discovered the next morning at the gate of the city of Milan which is called Roman. For God, who was preparing a strong support for His Catholic Church against His enemies and a tower of David against the face of Damascus, that is, the perfidy of the heretics, checked his flight. And when he had been found and was held in custody by the people, a report was sent to the most kind emperor, then Valentinian, who with very great joy realized the fact that the judges he sent out were being sought for the episcopacy. Probus the prefect rejoiced similarly, because his word was fulfilled in Ambrose, for he had said to him as he set out, when his orders were given to him as is the custom: “Go, act not as judge, but as a bishop.”
And so, while the result of the report was pending, he again attempted flight and for some time concealed himself on the estate of a certain honorable Leontinus. But, when the answer to the report came, he was handed over by this same Leontinus. For the order had been given to the deputy to insist on carrying out the matter, and, since he wished to fulfill the injunctions, he warned all by a published edict that, if they wished to take counsel for themselves and their property, they should hand over the man. Therefore, when he was handed over and had been taken to Milan and was aware of the will of God concerning himself and that he could no longer resist, he demanded that he should be baptized only by a Catholic bishop. For he was carefully guarding against the heresy of the Arians. Thus, when he was baptized, he is said to have fulfilled all the ecclesiastical offices, so that he was consecrated bishop on the eighth day with the greatest favor and joy on the part of all.

Paulinus, Life of Ambrose, 2-3
St. Ambrose of Milan, commemorated 7 December
troparion and icon at: http://www.comeandseeicons.com/a/cap09.htm
a near contemporary mosaic of St. Ambrose may be seen at: http://faculty.maxwell.syr.edu/gaddis/HST354/Feb25/ambrose.jpg