Maredudd ab Owain (died 999) was a King of Deheubarth, and through conquest also of Gwynedd and Powys, kingdoms in medieval Wales.
Maredudd was the son of Owain ap Hywel and the grandson of Hywel Dda. His father was king of Deheubarth before him. As Owain grew too old to lead in battle his son Maredudd took his place, and in 986 captured Gwynedd from Cadwallon ab Ieuaf. On Owain's death in 988 Maredudd also became ruler of Deheubarth. He may have controlled all Wales apart from Gwent and Morgannwg.
He is recorded as raiding Mercian settlements on the borders of Radnor and as paying a ransom of one penny a head to rescue some of his subjects who had been taken captive in Viking raids. Danish raids were a constant problem during Maredudd's reign. In 987 Godfrey Haroldson raided Anglesey, killing one thousand and carrying away two thousand as captives; Maredudd is supposed to have paid a huge ransom for the freedom of the hostages. Maredudd died in 999 and was described by the Brut y Tywysogion as "the most famous King of the Britons". Following his death, the throne of Gwynedd was recovered for the line of Idwal Foel by Cynan ap Hywel.
A daughter, Angharad, married Llywelyn ap Seisyll.