According to the 4th century historian Rufinus (x.9), who cites Frumentius' brother Edesius as his authority, as children (ca. 316) Frumentius and Edesius accompanied their uncle Metropius on a voyage to Ethiopia. When their ship stopped at one of the harbors of the Red Sea, people of the neighborhood massacred the whole crew, with the exception of the two boys, who were taken as slaves to the King of Axum. The two boys soon gained the favour of the king, who raised them to positions of trust, and shortly before his death, gave them their liberty. The widowed queen, however, prevailed upon them to remain at the court and assist her in the education of the young heir, Ezana, and in the administration of the kingdom during the prince's minority. They remained and (especially Frumentius) used their influence to spread Christianity. First they encouraged the Christian merchants present in the country to practise their faith openly; later they also converted some of the natives.
When Ezana came of age, Edesius returned to Tyre, where he stayed and was ordained a priest. Frumentius, on the other hand, eager for the conversion of Ethiopia, accompanied Edesius as far as Alexandria, where he requested Athanasius, Patriarch of Alexandria, to send a bishop and some priests to Ethiopia. By Athanasius' own account (Athanasius, Epistola ad Constantinum), he believed Frumentius the most suitable person for the job and consecrated him as bishop, traditionally in the year 328, or according to others, between 340-346. Frumentius returned to Ethiopia, erected his episcopal see at Axum, baptized King Ezana, who had meanwhile succeeded to the throne, built many churches, and spread Christianity throughout Ethiopia. The people called Frumentius Kesate Birhan (Revealer of Light) and Abba Salama (Father of Peace), and he became the first Abune — a title given to the head of the Ethiopian Church.
The most recent (2004) edition of the Roman Martyrology succintly states, "In Aethiopia, sancti Frumentii, episcopi, qui, primum ibi captivus, deinde, episcopus a sancto Athanasio ordinatus, Evangelium in ea regione propagavit [In Ethiopia, (the feast) of Saint Frumentius, bishop, who first was a captive there, and then, as a bishop ordained by Saint Athanasius, he spread the Gospel in that region]."
The Coptic Orthodox Church celebrates the feast of Frumentius on December 18, the Eastern Orthodox on November 30, and the Roman Catholic on October 27. Saint Frumentius is, however, venerated on August 1 in the Ethiopian Orthodox Tewahedo Church. Ethiopian tradition also credits him with the first Ge'ez translation of the New Testament.