He was a younger son of Robert de Brus, 5th Lord of Annandale and Isabella de Clare.
He held the manor of Caldecote in mesne lordship and a fee of Great Catworth, [1] both in Huntingdonshire, whom he held them of his father.
[2][3] William was summoned to provide military service in Scotland in 1295.
He is said to have married Elizabeth, daughter of Raymond de Sully.
Elizabeth married secondly William de Braose.