Marcellina was the only sister of St Ambrose of Milan, and older than he. She was born around 330 to 335, most likely at Trier, where her father was praetorian prefect (one of the empire's highest civil officials) of the Gauls. Even before her father died she had gone to Rome, her family's home, and there she gave up the world for a life of virginity, prayer and self-denial. On Christmas Day, probably in 353, Pope Liberius (pope 352–366) gave her the veil of a consecrated virgin. Ambrose preserved the advice the pope gave her that day.

After Ambrose became Bishop of Milan in 374 he called his sister there, and she became his zealous helper in spreading the religious life among the young women of Milan. In 377 he dedicated his books 'On Virgins' to her. She outlived her brother and died in 398 or soon after. She was buried in the crypt under the altar of the Ambrosian Basilica and honoured as a saint.

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The only sister of St. Ambrose of Milan, b. about 330-5; d. about 398. She was older than St. Ambrose, and was born most probably at Trier, where her father resided as praefectus praetorio Galliarum. Even before her father's death she went to Rome, the home of her family, and, before her mother's arrival at the capital with her two sons, had already forsaken the world, elected to live a life of Christian virginity, and devoted herself to the practice of piety and asceticism. On Christmas Day, probably in 353, she received the veil of consecrated virginity from the hand of Pope Liberius. The advice, which the pope addressed to her on this occasion, has been preserved by St. Ambrose (De virginibus, III, i-iii), especially emphasized being the obligations of Christian virgins to preserve virginal purity. After Ambrose had become Bishop of Milan (374), he summoned his sister thither, and found in her a zealous assistant in fostering and extending the ascetic life among the maidens of Milan. To her Ambrose dedicated his work on viriginity, written in 377 ("Libri III de virginibus ad Marcellinam" in P.L. XVI, 187-232). Marcellina survived her brother, and died in 398 or shortly afterwards. She also was buried in the crypt under the altar of the Ambrosian Basilica, and was honoured as a saint. Her feast is celebrated on 17 July.

Laudatio Marcellinae in MOMBRITIUS, SS., II, 95-7; Acta SS., IV, July, 231-8; BlRAGHI, Vita della vergine romana-milanese S. Marcellina, sorella di S. Ambrogio (4th ed., Milan. 1889), SEPTIMUS A LANDE ET ALANUS DE MACULANIS, Dissert. hist. de tumulo S. Marcellinae virg. sororis S. Ambrosii in eiusdem imperiali basilica humanae (Milan, 1725). see also bibliography to AMBROSE, SAINT.