Although William Pole and John Prince both stated him to be the son of another Sir John Wadham of Edge in the parish of Branscombe Devon, his modern History of Parliament biographer suggests he may have been the son, rather than the nephew perhaps, of Gilbert Wadham (c.1320-1383) of Wadham, who in 1383 quitclaimed to him a rent in the manor of Wadham or Wadeham in the parish of Knowstone, between Exmoor and South Molton, from which the family originally took their name, and where, according to Sir William Pole, they had lived from at least the reign of King Edward I (1272-1307).