The son of Roger D'arcy and Isabel d’Aton, he may have been born at Knaith, Lincolnshire, circa 1280. Darcy became one of the most trusted advisors to Edward III of England and was appointed High Sheriff of Nottinghamshire, Derbyshire and the Royal Forests in 1319, High Sheriff of Lancashire in 1323 and High Sheriff of Yorkshire in 1327. He served as Member of Parliament for Nottinghamshire in 1320. He was summoned to Parliament in 1331, 1333 and 1341 as "Johanni D'arcy le Cosin".