He is credited with founding Llangrannog, Ceredigion, Wales[1] and St Carantoc's Church, Crantock.

Carantoc's is one of five insular saints' lives and two Breton ones that mention Arthur in contexts that may be independent of Geoffrey of Monmouth's Historia Regum Britanniae.

He probably moved to Cornwall before preaching for some time in Ireland, around Dulane in County Meath and Inis-Baithen in Leinster.

[4] In the most famous incident of Carantoc's life, the saint, having returned to Wales, crossed the Bristol Channel, looking for his portable altar.

Carantoc was eventually obliged to defeat a ferocious dragon in order to retrieve his altar and, in return, was given land at nearby Carhampton to found a monastery.