In Ceredigion, he set about the task of converting the locals to Christianity from a monastic centre which he established at Llandyfriog. But, not long after his arrival, he was persuaded, by another angelic visitor, to sail away to Italy with 168 followers. The journey was rough and not helped by their boat being attacked by an enormous sea-creature. Eventually the travellers landed in Cornwall - possibly at Padstow Harbour near St.Breock - where they encountered a pagan king named Conan. Brioc soon converted the monarch and the rest of the Royal Court, before pressing on into Europe. He crossed the Channel to Brittany and landed at Le Conquest in Plouguerneau (Finistère). From here, the companions moved down the River Jaudy and founded a monastery at Tréguier. However, hearing of a pestilence ravaging his Wales, Brioc decided he must return home. He left his new church in the hands of his 'nephew', Tudgual, and delivered his people from their plague by advising the people to confess their sins.

Returning once more to Brittany, Brioc decided to try his luck in new territories. With eighty-four companions, he travelled to the mouth of the River Gouet. The local king, Riwal, was not happy with these strangers arriving in his Kingdom but, upon meeting them, realized that their leader, Brioc, was his own cousin. The king gave Brioc his home, the 'Hall of the Champ du Rouvre' and removed the Royal court to nearby Licelion in Hillion parish. The saint was obliged to visit King Childebert of the Franks in Paris in order to confirm this grant, and he travelled with St. Samson and other bishops. Slowly, Brioc's men built a monastic complex around their new hall and this become the great monastery of St. Brieuc.

St. Brioc died on 1st May, but it is difficult to say exactly when. St. German of Paris was bishop there between AD 555 & 576. St.Germanus of Auxerre died in AD 448. Conan Meriadog was King of Dumnonia (including Cornwall) in the mid-4th century. St. Tudwal lived in the mid-6th century. Riwal was King of Domnonée (in Brittany) in the early 6th century. St. Patrick lived in the late 5th century. St. Illtud lived in the early 6th century. St. Samson lived in the mid-6th century. King Childebert ruled from AD 511 to 558. A lifetime covering the early to mid-6th century seems likely for Brioc. Like King Riwal, St. Tugdual appears to have been St. Brioc's cousin, rather than his nephew, since he was actually Riwal's maternal nephew. The family relationships would indicate that Brioc's mother, Eldruda, was a Princess of the Royal House of Domnonée.