Dunstaple was probably born in Dunstable, Bedfordshire around 1390. We know very little about his life. He was well educated and he worked for the Duke of Bedford who was the fourth son of Henry IV and brother of Henry V. He may have spent some time in France because the duke was Regent of France from 1423 to 1429, and then Governor of Normandy from 1429 to his death in 1435. Dunstaple owned property in Normandy, and also in Cambridgeshire, Essex and London, according to tax records of 1436. He also worked for the Duke of Gloucester.