John Foxley's parentage is unknown. There is no evidence of any connection with the ancient house of Foxley of Foxley and Blakesley in Northamptonshire as has sometimes been conjectured, for the arms are quite different. John became a lawyer of some repute and  then a judge. In 1308, he was granted custody of the temporalities of the vacant abbacy of Westminster. On 28th February the following year, he was constituted a Baron of the Exchequer in place of the late Roger de Hegham, and he may also have been knighted around this time. Besides performing the duties of that court, he was frequently named in commissions, and appointed to take inquests by the parliament, and called upon to act as a justice of assize and of oyer and terminer in the provinces; and also in the perambulations of the forests. Towards the end of his career, he was appointed to administer the estate of the magnificent Anthony Beck, Bishop of Durham. He resigned his Exchequer post in 1322, when he was replaced by Roger Beler, but continued to be employed in a judicial character on his home ground in the counties of Oxfordshire and Berkshire.

Foxley had married a lady named Constance in the earliest years of the 14th century. She appears to have been the heiress of the De Bramshill family from Bramshill in Hampshire, which manor they had inherited by 1306 when they obtained permission from the Bishop of Winchester to have divine service held in their chapel there. Eleven years later, the King granted them free warren also. Foxley's long legal career and the favour of kings, had brought him much wealth with which he was able to use to add to these land holdings. Among proofs of the Royal patronage were life-interests in the the manors of Rendcomb in Gloucestershire, and other lands and tenements in East Bridgeford in Nottinghamshire and Saxby in Leicestershire. Although, on one occasion, Foxley was fined one mark, because he had taken possession of certain land in Berkshire without the king's license. Chief amongst his purchases was the manor of Pokemere at Bray in Berkshire (soon to be renamed Foxley's) which he made his home in 1313 and where he was granted license to create a deer park in 1321. When John died four years later, he was therefore possessed of considerable property in the counties of Hampshire, Berkshire, Buckinghamshire and elsewhere. He was succeeded in them by his son, Thomas.