Born of a distinguished family towards the close of the sixth or the beginning of the seventh century, at Guldendal, Switzerland; died c.670. Following the death of his mother, he, with his father, joined the monastery of Luxeuil in the Diocese of Besançon, probably about 615. Under the direction of Eustachius, Omer studied the Scriptures, in which he acquired remarkable proficiency. When King Dagobert requested the appointment of a bishop important city of Terouenne, the capital of the ancient territory of the Morini in Belgic Gaul, he was appointed and consecrated in 637.
Though the Morini had received the Faith from Saints Fuscian and Victoricus, and later Antmund and Adelbert, nearly every vestige of Christianity had disappeared. When Saint Omer entered upon his episcopal duties the Abbot of Luxeuil sent to his assistance several monks, among whom are mentioned Saints Bertin, Mommolin, and Ebertran, and Saint Omer had the satisfaction of seeing the true religion firmly established in a short time. About 654 he founded the Abbey of Saint Peter (now Saint Bertin’s) in Sithiu, soon to equal if not surpass the old monastery of Luxeuil for the number of learned and zealous men educated there. Several years later he erected the Church of Our Lady of Sithiu, with a small monastery adjoining, which he turned over to the monks of Saint Bertin. The exact date of his death is unknown, but he is believed to have died about the year 670. The place of his burial is uncertain; most probably he was laid to rest in the church of Our Lady which is now the cathedral of Saint Omer’s. His feast is celebrated on 9 September – when and by whom he was to the altar cannot be ascertained.