Almost all that is known of Saint Boisil is learned from Bede. He derived his information from Sigfrid, a monk of Jarrow, who had previously been trained by Boisil at Melrose. St Boisil's fame is mainly due to his connection with his great pupil, Saint Cuthbert, but it is plain that the master was worthy of the disciple. Contemporaries were deeply impressed with Boisil's supernatural intuitions.
When Cuthbert presented himself at Melrose, then part of Anglo-Saxon Northumbria, Boisil exclaimed "Behold a servant of the Lord", and he obtained leave from Abbot Eata to receive him into the community at once. When in the great pestilence of 664 Cuthbert was stricken down, Boisil declared he would certainly recover. Somewhat later Boisil himself as he had foretold three years before, fell a victim to this terrible epidemic, but before the end came he predicted that Cuthbert would become a bishop and would effect great things for the Church.
After his death, Boisil appeared twice in a vision to his former disciple, Bishop Ecgberht. He is believed, on somewhat dubious authority, to have written certain theological works, but they have not been preserved. St Boswells in Roxburghshire commemorates his name. His relics, like those of Saint Bede, were carried off to Durham in the 11th century by the priest, Alfred Westow. In the early Calendars, his day is assigned to 23 February. The Bollandists treat of him on 9 September but his feast is generally accepted as 7 July, with a translation on 8 June.