He was born on the family estate of Pendrea in St Buryan, Cornwall. He left Exeter College, Oxford without taking a degree, and entered Lincoln's Inn in 1594. From 1603 until his death he was elected, with one exception, to each parliament, sitting invariably for a constituency of his native county. For several years his sympathies were in antagonism to the court party. Yet every commission that was appointed numbered Noy among its members, and even those who were opposed to him in politics acknowledged his learning.
A few years before his death he changed political allegiance, went over to the side of the court, and in October 1631 he was created Attorney-general, but was never knighted. It was through his advice that the impost of ship money was levied, resulting in a controversy that helped trigger the English Civil War. Noy suffered from stones, and died in great pain; he was buried at New Brentford church.
His principal works are On the Grounds and Maxims of the Laws of this Kingdom (1641) and The Compleat Lawyer (1661).