[1][2] His family had experienced the loss of their patrimony including Lyonshall Castle, and his father did not retain the barony granted to his grandfather, William Devereux.
John's youth was spent in close alliance with his older brother, Stephen Devereux of Bodenham and Burghope, in trying to revive the family fortunes.
John Devereux is identified as a witness to a grant of a croft in 1317 in the town of la More (Hereford) by Thomas Swonild to Thomas de Houton (and his sons, Walter and Hugh) between the lands of his father, Sir Walter Devereux, and the Tyne brook.
[3] On 11 December 1323 a commission of oyer and terminer was called to investigate a complaint by Richard de Portes that ‘John Deueres’ was among a group of men that assaulted him at Gloucester, and broke the gates and doors of his houses at Bromesberwe (Yockeford), and Dunhampton (county Gloucester), cut down his trees and carried them and other goods away.
[9] John Devereux participated in Edward III's invasion of France in 1346 as part of the retinue of Laurence Hastings, 1st Earl of Pembroke, and was present at the Battle of Crécy.