Very little at all is known about Saint Nicholas's historical life. Any writings Nicholas himself may have produced have been lost and he is not mentioned by any contemporary chroniclers. This is not surprising, since Nicholas lived during a turbulent time in Roman history. Furthermore, all written records were kept on papyrus or parchment, which were less durable than modern paper, and texts needed to be periodically recopied by hand onto new material in order to be preserved. The earliest mentions of Saint Nicholas indicate that, by the sixth century, his cult was already well-established. Less than two hundred years after Saint Nicholas's probable death, the Eastern Emperor Theodosius II (ruled 401–450) ordered the building of the Church of Saint Nicholas in Myra, which thereby preserves an early mention of his name. The Byzantine historian Procopius also mentions that the Emperor Justinian I (ruled 527–565) renovated churches in Constantinople dedicated to Saint Nicholas and Saint Priscus, which may have originally been built as early as c. 490.
Nicholas's name also occurs as "Nicholas of Myra of Lycia" on the tenth line of a list of attendees at the Council of Nicaea recorded by the historian Theodoret in the Historiae Ecclesiasticae Tripartitae Epitome, written sometime between 510 and 515. A single, offhand mention of Nicholas of Myra also occurs in the biography of another saint, Saint Nicholas of Sion, who apparently took the name "Nicholas" to honor him. The Life of Saint Nicholas of Sion, written around 250 years after Nicholas of Myra's death, briefly mentions Nicholas of Sion visiting Nicholas's tomb to pay homage to him. According to Jeremy Seal, the fact that Nicholas had a tomb that could be visited serves as the almost solitary definitive proof that he was a real historical figure.
In his treatise De statu animarum post mortem (written c. 583), the theologian
Eustratius of Constantinople cites Saint Nicholas of Myra's miracle of the three counts as evidence that souls may work independent from the body. Eustratius credits a lost Life of Saint Nicholas as his source. Nearly all the sources Eustratius references date from the late fourth century to early fifth century, indicating the Life of Saint Nicholas to which he refers was probably written during this time period, shortly after Nicholas's death. The earliest complete account of Nicholas's life that has survived to the present is a Life of Saint Nicholas, written in the early ninth century by
Michael the Archimandrite (814–842), nearly 500 years after Nicholas's probable death.
Despite its extremely late date, Michael the Archimandrite's Life of Saint Nicholas is believed to heavily rely on older written sources and oral traditions. The identity and reliability of these sources, however, remains uncertain. Catholic historian D. L. Cann and medievalist Charles W. Jones both consider Michael the Archimandrite's Life the only account of Saint Nicholas that is likely to contain any historical truth. Jona Lendering, a Dutch historian of classical antiquity, notes that Michael the Archimandrite's Life does not contain a "conversion narrative", which was unusual for saints' lives of the period when it was written. He therefore argues that it is possible Michael the Archimandrite may have been relying on a source written before conversion narratives became popular, which would be a positive indication of that source's reliability. He also notes, however, that many of the stories recounted by Michael the Archimandrite closely resemble stories told about the first-century AD Neopythagorean philosopher Apollonius of Tyana in the Life of Apollonius of Tyana, an eight-volume biography of him written in the early third century by the Greek writer Philostratus. Christian storytellers were known to adapt older pagan legends and attribute them to Christian saints. Because Apollonius's hometown of Tyana was not far from Myra, it is highly probable that many popular stories about him became attached to Saint Nicholas.