His father was a native of Grantchester in Cambridgeshire: his surname is an early form of the town's name (which appears as Grantesete and Grauntsethe in Domesday Book).
In 1317 he, his wife and her mother compounded with Dublin Corporation for the numerous fines owed by his late father-in-law, who was notorious for corruption, especially in regard to his grossly dishonest mismanagement of the collection of the murage i.e.the toll for the upkeep of the city walls.
[3] John continued to practice law and was acting as legal adviser to the Harold family, who were tenants of Rathfarnham Castle, in 1320.
He was charged with attempting to subvert the Royal authority in favour of that of the Pope, deprived of office, imprisoned and heavily fined.
[3] King Edward III however soon granted him a royal pardon: he was restored to office, and shortly afterwards transferred to a more senior position,[8] and in 1331 obtained an annulment of the judgment against him.
[3] He complained to the Crown that these lands had been so ravaged during "the coming of the Scots" (the Bruce Invasion of 1315-18) that he was unable to work them profitably.
[10] He was also appointed Seneschal of Newcastle Lyons in south County Dublin in 1327, on his own petition "with the same fee payable as in time past".
[6] In 1334 he petitioned the English Chancery to execute a recognisance (a conditional pledge to pay money) entered into in his favour by John FitzReginald.
In return for his benefactions to the Priory, he was given a large suite of servants to attend to his needs, three horses and the right to dine at the Prior's table.