Knight of Herstmonceux, Sussex, of White Waltham, Berkshire, of Ascot in Great Milton, Oxfordshire. Sheriff of Surrey and Sussex.
Younger son of Sir William de Fiennes and Joan de Say, grandson of Sir John de Fiennes and Maud de Monceux, Sir Geoffrey de Say and Maud de Beauchamp.
Husband of Elizabeth Batisford, daughter and co-heiress of William Batisford of Buckholt in Bexhill, Sussex and Margery de Peplesham, daughter of Simon. They had two sons, Sir Roger and James.
In 1398 they were granted a papal indult for plenary remission (forgiveness for sins), and in 1402 William assisted in compiling the ordinances for Pevensey Marsh.
Elizabeth Batisford Fiennes