Meurig took over the Gwent throne upon his father's abdication. According to tradition, Tewdrig became a hermit at Tintern, but later came to the assistance of Meurig, and they repelled the invading Saxons in a battle at Pont y Saeson (Bridge of the Saxons). Tewdrig died after the battle, and Meurig buried him at Mathern, having an oratory built there and giving the surrounding land (including the area of the later village of Pwllmeyric, named after Meurig), in his memory to the bishops of Llandaff.
Meurig reunited his kingdom with Ergyng (Archenfield) by marrying Onbrawst, the daughter of Gwrgan Fawr (the Great), the ruler of that kingdom. He was later claimed to have been a great patron of the ecclesiastical centre at Llandaff, where he is said to be buried.
He was the father of Athrwys ap Meurig, one of a number of figures that researchers have claimed as the "real King Arthur". Athrwys is believed to have pre-deceased Meurig, who was succeeded by his grandsons, Ithel and Morgan Mwynfawr.