Dafydd ap Llywelyn (c. 1208–February 25, 1246) was Prince of Gwynedd from 1240 to 1246.

He was the only legitimate son of Llywelyn the Great by his wife, Joan (daughter of King John). Recognised as Prince of Wales by his uncle King Henry III of England in 1220 (the first to hold this title officially), he ruled Gwynedd following his father's death in 1240, despite the rival claims of his half-brother, Gruffydd ap Llywelyn, who died trying to escape from the Tower of London in early 1244. Dafydd's revolt of 1244 against the Crown was only a temporary success, and his sudden death led to disorder, his marriage to Isabella de Breos having failed to produce an heir.