The 'Life of St. Euddogwy' tells how Budic took refuge at the court of King Aircol Lawhir of Dyfed. There, he met and married his wife, Anawfedd, the sister of St. Teilo. During their time in Britain, Anowed gave birth to at least two sons, Ysfael and Tyfái. During her last pregnancy (when she supposedly bore Euddogwy), however, messengers arrived announcing that the usurper in Brittany was dead. His people desired Budic to return as their King and he eagerly obliged. The intruder was apparently Marchil Chillon who is known to have beseiged Nantes in 497.

It was traditionally during Budic's reign that the Breton armies first gained a reputation for being invincible on horseback, thanks to St. Teilo. During a visit to his brother-in-law's Breton Court, legends says that the saint was persuaded by Budic to rid his lands of a terrible dragon that was terrorising the countryside. With much prayer, Teilo was able to subdue the beast and he tied it to a rock in the Sea. Afraid that it would return without Teilo's protection, Budic installed his brother-in-law as Bishop of Dol. Teilo entered the city upon a divine white steed given to him by an angel. This, he later presented to the King with the promise that his cavalry would always be victorious in battle.

Geoffrey of Monmouth knew of this monarch and claimed that he married the sister of High-King Arthur of Britain. His wife is usually assumed to have been Anna, but there are indications that Elaine (Elen) was meant. Budic's title of Emyr was probably corrupted to Nentres, Geoffrey's name for Elaine's husband, who was then mistakenly allocated a settlement in the the realm of Anna's husband called Garlot (from Caer-Lot). Geoffrey's Budic had a son named Hoel Mawr (the Great). In later Arthurian literature, Budic was probably turned into King Ban of Benwick (sometimes called Brittany).

It is not impossible that Geoffrey had access to some lost tradition, for other sources indicate that Budic had older children, perhaps from an earlier marriage: Teudric, Meliau, Rivod and ancestors of a number of saints. He made an alliance with King Macliau of Broerec and agreed that each would protect the other's heir and their inheritance if something should happen to the father. When Budic died, however, Macliau overran Cornouaille and the former's eldest son, Teudric, was forced to flee abroad.

Records of Budic date back to the 11th century. He is generally considered likely to be historic.