His father Hamelin granted him the manor of Appleby, North Lincolnshire.
His first tenure of office as Lord Warden of the Cinque Ports began in 1204, and lasted until 1206. He was also a Warden of Welch marches between 1208-1213.
William was one of the few barons who remained loyal to King John (who was his cousin) during the king's difficulties with the barons, when they sought for the French prince to assume the English throne, and is listed as one of those who advised John to accede to the Magna Carta. His allegiance only faltered a few times when the king's cause looked hopeless.
In March, 1217 he again demonstrated his loyalty to England by supporting the young King Henry III, he was also responsible for the establishment of the cathedral at Salisbury.
Between the years 1200-1208, and during 1213-1226 he was to serve as the Sheriff of Wiltshire. In 1214 he was again appointed Lord Warden of the Cinque Ports.
|Offspring of William de Warenne and Maud Marshal (1192-1248)|
|John de Warenne (1231-1304)||1231||29 September 1304|| Alice de Lusignan (1224-1256)|
|Isabel de Warenne (c1228-1282)||1228||1282|| Hugh of Aubigny (c1215-1243)|
Namesakes of William de Warenne (1166-1240)
Common ancestors of William de Warenne (1166-1240) and Maud Marshal (1192-1248)
- Adelaide de Vermandois (1064-1120)
- Elizabeth de Vermandois (c1081-1131)
- Hugh de Vermandois (1053-1101)