Marcellina was born in Trier, Gaul around the year 330 as a member of a Catholic family. She was eldest sister to saint Satyrus and Saint Ambrose of Milan. After the death of her father, who was prefect of the Gauls, she moved to Rome with her pious mother and brothers.
Marcellina was discreet beyond her years, and from her cradle sought with her whole heart the only thing for which she was created and sent into the world. Being charged at Rome with the education of her two brothers, she inspired them, by words and example, with an ardent thirst of virtue. She taught them that nobleness of blood cannot enhance merit, nor make men more illustrious unless they despise it; and that learning is an unpardonable crime and folly, if by it a man should desire to know everything that is in heaven and earth but himself; for with the true knowledge of ourselves are all our studies to begin and end, if we desire to render them in any degree advantageous to ourselves. She kindled in their tender breasts a vehement desire, not of the show of virtue, but to become truly virtuous. In her whole conduct all her view was only the glory of God.
She was still young back then, when she received the veil of consecrated virginity from Pope Liberius on Christmas day in 353 in front of many people and then devoted herself to the practice of piety and asceticism. The pope, in a short discourse on that occasion, exhorted her frequently to love only our Lord Jesus Christ, the chaste spouse of her soul, to live in continual abstinence, mortification, silence, and prayer, and always to behave herself in the church with the utmost respect and awe. He mentioned to her the page of Alexander the Great, who, for fear of disturbing the solemnity of a heathenish sacrifice by shaking off his hand a piece of melted wax that had fallen upon it, let it burn him to the bone.
She made it a point to pass her younger brothers the “desire not to express their virtue, but to become truly virtuous.” This life she led call for continual abstinence, dedication to prayer, strict fasting, etc. This life chosen by Saint Marcellina is one of her great sacrifice.
Marcellina in her practice went beyond the most perfect lessons. She fasted every day till evening; and sometimes passed whole days without eating. She never touched any fare but what was of the coarsest kinds, and drank only water. She never laid herself down to rest till quite overcome with sleep. The greater part both of the day and night she devoted to prayer, pious reading, and tears of divine love and compunction. St. Ambrose advised her in the decline of her life to moderate her austerities, but always to redouble her fervour in tears and holy prayer, especially in reciting often the psalms, the Lord’s prayer, and likewise the creed, which he calls the seal of a Christian, and the guard of our hearts.
Upon St. Ambrose being made Bishop of Milan in 374, he summoned Marcellina to be his assistant. She was responsible for fostering and extending the ascetic life among the maidens of Milan. In 377, St. Ambrose dedicated his writings on virginity to her.
Marcellina stayed in Rome after the death of her mother, living not in a nunnery but in a private house with one fervent virgin, the faithful companion of all her holy exercises. She survived St. Ambrose by only a year, dying in 398. Honored as a saint, She was buried in the crypt under the altar of the Ambrosian Basilica in Milan.