Adeodatus was the offspring of the sexual relationship of Augustine with a woman who remained unnamed throughout his Confessions and all his other writings - a de facto union that faithfully lasted for thirteen years. It began in 372 at Carthage and ended in about 385 in Milan. In the year 372 this concubine bore Augustine a son whom they named Adeodatus, The conception of Adeodatus was described by Augustine as being unplanned, hence the child was "given by God" in a number of senses of the phrase. Augustine felt he contributed nothing to the boy’s making but his fault. Augustine was then a Manichee, for whom procreation was one of the worst sins possible.

The family of three lived in Carthage until 374, when they moved to Thagaste, the home town of Augustine. There he opened a simple school that taught grammar. They moved back to Carthage again in 376, where Augustine now felt confident enough to open a more formal school of rhetoric. He persisted there for eight years, as Adeodatus approached adolescence. In 383 the young family moved to Rome, where once again they met some friends from North Africa, including Alypius. In 384 they moved to Milan. The mother of Augustine, Monica, joined them in Milan in 385. She set about arranging a marriage for him with a Catholic woman of an appropriate rank and means so as to promote his career. For Augustine, this meant expelling his faithful partner of fourteen years.

This parting was emotionally difficult for both of them. Whereas the partner was sent back to North Africa, Adeodatus remained with his father and with Monica, his grandmother. Indeed, father and son prepared for baptism together, and were baptised, along with Alypius, at Easter 387 by the Bishop of Milan, Ambrose. When Augustine had become a Christian, Adeodatus was a teenager himself. Their personal and spiritual relationship was a very close one.  Adeodatus for Augustine was a wonder - literally a "gift from God" (which is how the Latin name, Adeodatus, translates into English). He said Adeodatus was awe-inspiring, and lived a life of such purity that no one need fear for him or for his eternal salvation.  In the year 387 Adeodatus was present with Augustine and Monica at the port town of Ostia to await a ship back to North Africa. He witnessed the death of Monica, his grandmother.

In writing about the event in Book Nine of Confessions, Augustine commented that Adeodatus had to be consoled afterwards. The weeping of Adeodatus made Augustine also want to weep, but he held back his own tears until he was alone. The journey to North Africa was then postponed for over a year, which father and son spent together in Rome.

Adeodatus accompanied Augustine back to Tagsate, where Augustine began a lay Christian community. Adeodatus was a member of this initial community. The early writings of Augustine from this period include his intellectual dialogues with his son, firstly in De Beata Vita ("The Blessed Life") at Cassiciacum before tehey were baptised together. Secondly, Adeodatus appeared in the book by Augustine named De magistro ("On the Teacher") as an exceptionally intelligent youth aged seventeen years, and as a close friend of his father.

In the year 390 Adeodatus died before reaching his eighteenth birthday. He died at the very same age Augustine had been when Adeodatus was born. The early and untimely death of Adeodatus was a number of close deaths that caused Augustine great sadness. His Confessions reveals his numerous tears on various subsequent occasions when his recalling of Adeodatus prompted Augustine to meditate upon God's plan of salvation, and on the fickleness of human life.

Adeodatus had been the object of the tender solicitude of his father. Although Augustine openly wrote about Adeodatus in his Confessions, little mention was made of him from the time of the writing of Augustine's biographer, Possidius, until the era of Jordan of Saxony O.S.A.  in c. 1299 - c. 1380. This silence about Adeodatus and his concubine mother was possibly because they were startling reminders of the relatively-unbridled lust of Augustine in his early years - something that also was passed over by centuries of Christian writers.

These authors included members of the Order of Saint Augustine, who desired to promote the identity of Augustine as his being an exemplar for religious community life rather than as one who was fallable. 

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