The date of his birth is now lost yet we know that he was related to a predecessor in the See, Archbishop Walter Giffard, who paid for the young Greenfield's Oxford education in the year 1269.

Giffard instructed that his bailiff at Churchdown (near Gloucester), "...to pay to Roger the miller of Oxford twenty shillings, for our kinsman William of Greenfield while he is studying there, because it would be difficult for us to send the money to him on account of the perils of the ways".

[2] Greenfield was strongly commended to the pope and cardinals by the King, who told them of his "...wisdom in council, industry, literary knowledge, and usefulness to the state".

In an attempt to free himself from the Italian money lenders he exacted aids from the clergy, and borrowed from many church dignitaries in the north of England.

Greenfield died at his palace of Cawood on 6 December 1315,[2] and was buried in the eastern part of the north transept of York Minster, where his monument still remains.