St. Gildas was most likely born around 517 in North England or Wales. He most likely had multiple siblings. His father's name was Cau (or Nau), and he was of noble descent. Writings exist that indicate King Arthur (d. 537 AD) murdered one of his brothers, Cuil (or Hueil), and it seems that Gildas may have pardoned Arthur for the deed.

The life of St. Gildas the Wise is told in two different ways, and they both give different accounts. He was born during a period when Rome's heyday had passed into Britain. Maximus had withdrawn the permanent legions and used them to take control of Rome and crowned himself Emperor.

Known for his piety and education in particular, Gildas was not hesitant to publicly criticize modern monarchs during a period when libel was dealt with with a sword rather than a court ruling.

Gildas was an extremely austere hermit who spent many years living on Flatholm Island in the Bristol Channel. He made his name there for that strange kind of holiness that comes from great solitude and self-denial, typical of the Celtic people. The Welsh claim that at this same period, he also preached to St. David's mother Nemata, who was expecting the Saint.

He penned a work titled De Excidio Britanniae (The Destruction of Britain) around 547. This is a brief account of the island's pre-Roman history in which he condemns the island's rulers for their lack of morality and holds them accountable for the demise of British civilization through their faults and those of their descendants. The book was clearly intended to be a morality story.

In addition, he composed the lengthier Epistle, a collection of sermons criticizing the moral slackness of the clergy and governing bodies. Gildas demonstrates his familiarity with the Bible and other classic literature through them.

In addition, he was a highly effective preacher. Many people on the island were converted as a result of his trips to Ireland and the outstanding missionary work he accomplished there. He may also have been the one to introduce anchorite rituals to the monks residing there.

After that, he left Llancarfan and moved to Rhuys in Brittany, where he established a monastery. Of his writings on monastic administration (among the oldest recognized in the Christian Church), only the so-called Penitential—a manual for abbots on imposing punishment—remains extant.

He died in Rhuys circa 571.

He is recognized as one of the early English Church's most important figures. His writings continued to have an impact well into the Middle Ages, especially in the Celtic Church. Being the first British author whose works have survived largely undamaged, he is also significant to us now.

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