He was a direct descendant in an unbroken male line of Robert de Courtenay (d.1242), son of Reginald II de Courtenay (d.1194) by his wife Hawise de Curcy (d.1219), heiress of the feudal barony of Okehampton in Devon. Robert married Mary de Vernon, daughter of William de Redvers, 5th Earl of Devon (d.1217), feudal baron of Plympton in Devon. From this marriage the Courtenays later inherited the barony of Plympton in 1293 and in 1335 were declared Earls of Devon. The House of Courtenay were not Normans who "came over with William the Conqueror", as did much of the ancient English aristocracy, but were Frenchmen who were seated within the Kingdom of France, one of whom came to England some time after the Norman Conquest, having had his lands seized by the French king.