Maredudd ab Owain (died c. 999) was a Welsh monarch, ruling in Gwynedd, Deheubarth and Powys. A member of the House of Dinefwr, his patrimony was the kingdom of Deheubarth comprising the southern realms of Dyfed and Seisyllwg. Upon the death of his father King Owain ap Hywel Dda around 988, he also inherited the kingdoms of Gwynedd and Powys, which he had conquered for his father. He was counted among the Kings of the Britons by the Chronicle of the Princes.
Maredudd was the younger son of King Owain ap Hywel Dda of Deheubarth and the grandson of King Hywel Dda. Owain had inherited the kingdom through the early death of his brothers and Maredudd, too, came to the throne through the death of his elder brother Einion around 984. Around 986, Maredudd captured Gwynedd from its king Cadwallon ab Ieuaf. He may have controlled all Wales apart from Gwent and Morgannwg.