Prince Judwal’s father, Prince Jonas, was killed when he was still a lad and he was brought up by his apparently kind and generous step-father, King Conomor alias Mark of Cerniw & Poher. One day, however, Judwal’s mother dreamt that all the kings in Brittany paid homage to her son while he sat upon a mountain. The King Conomor, who had in fact murdered Judwal’s father, became highly disturbed by such a supremacy dream and plotted to his newfound family. However, Judwal and his mother got wind of the plot and escaped to St. Lunaire's monastery, from where the holy man sent them on to King Childebert in Paris.

Judwal grew up at the Frankish Court, and when he reached adulthood in the mid-6th century, he was encouraged by St. Samson to return to Domnonée and claim his inheritance. People rallied to his cause from all over the principality and he soon had an army of followers large enough to confront Conomor. They clashed in battle on three occasions and, each time, Judwal was victorious. He quickly secured his position on the Domnonian throne, while Conomor fled across the Channel to Cerniw.

He was eventually succeeded by his son, Judhael, and his many grandsons.