Gray was born in Canterbury, Kent and after some basic schooling, he was apprenticed to his father (subsequently his elder brother) in the cloth-dyeing trade. His interests, however, lay with natural science and particularly with astronomy, and he managed to educate himself in these developing disciplines, mainly through wealth friends in the district who gave him access to their libraries and scientific instruments. Science was very much a rich-man's hobby at this time.
He ground his own lenses and constructed his own telescope, and with this instrument he made a number of minor discoveries (mainly in the area of sunspots), gaining a reputation for accuracy in his observations. Some of his reports were published by the Royal Society through the agency of a friend Henry Hunt who was a member of the Society's secretarial staff.
Some of this material came to the notice of John Flamsteed (who was related to some Kent friends of Gray) the first English Astronomer-Royal, who was building the new observatory at Greenwich. Flamsteed was attempting to construct a detailed and accurate star-map of the heavens, in the hope that this would eventually solve the problem of longitude determination for ocean navigators. Gray helped him with many of the observations and calculations (possibly without being paid).
Gray and Flamsteed became constant correspondents and friends, and this seems to have create problems for Gray in being accepted formally into the world of science. Flamsteed was involved in a prolonged dispute (more like a 'heated battle') with Sir Isaac Newton over access to preliminary star-chart data. This boiled over and became a factional war in the Royal Society, which Newton dominated (virtually excluding Flamsteed and his associates) for decades.
Gray worked for a while on the second English observatory being built at Cambridge, but it was badly managed by Newton's friend and associate Coates, and finally the project collapsed leaving Gray with little option but to return to his dyeing trade in Canterbury. However his health was a problem, and before long he was in London assisting Dr John Desaguliers, one of the Royal Society' demonstrators, who gave lectures around the country (and on the Continent) about new scientific discoveries. Gray was probably not paid, but provided with accommodation only.
Poverty intervened for Gray, and through the efforts of (now Sir) John Flamsteed and Sir Hans Sloane (later President of the Royal Society) he managed to obtain a pensioned position at the Charterhouse in London (a home for desititute gentlemen who had served their country). During this time he began experimenting again with static electricity, using a glass-tube as a friction generator.
One night, in his Charterhouse rooms, he noticed that the cork in the end of his tube (needed to keep moisure and dust out) generated an attractive force on small pieces of paper and chaff when the tube was rubbed. When he extended the cork with a small fir stick plugged into the middle the charge was evident at the end of the stick. So he tried longer sticks, and finally he added a length of thread terminating with an ivory ball. In the process he had discovered that the "electric virtue" would carry over distance, and that the ivory ball would act to attract light objects as if it were the electrified glass tube.
Over the next few days he extended the reach of his thread-wire (he only had a short piece of wire, and didn't understand the significance of metal as a conductor), and on a number of visits to wealthy friends in Kent (Flamsteed's relatives, and the Reverend Granville Wheler) he extended his experiments through thread laced up and down through the large rooms of their manor houses, then down from the tower to the courtyard, and eventually out, across the paddocks to a distance of 800 feet.
In the process, Gray and Wheler discovered the importance of insulating their thread 'wire' from earth contact, using silk (which is drier, and therefore less of a conductor than the hemp pack-thread they used as their main conductor). They noticed that wire supports to the pack-thread leaked away the electrical charge, and discovered that electricity was carried around bends in the 'wire' and that it didn't seem to be helped any by gravity when the thread was dropped from the tower.
From these experiments came an understanding of the role played by conductors and insulators (names applied by John Desaguliers). Charles DuFay, a French scientist, visited Gray and Wheler in 1732, saw the experiment, and returned to France where he formulated the first comprehensive theory of electricity called the "two-fluid" theory. This was taken up by his associate, the Abbe Nollet, and opposed (to a degree) by Benjamin Franklin's group in Philadelphia -- where Franklin and English experimenters Beavis and Watson, had devised a single-fluid/two-state theory (later given the terms +ve and -ve by Watson) which eventually prevailed.
Gray went on to make more electrical experiments, including inducing electrical polarity in suspended objects (he may have invented the famous "Flying Boy" demonstration - a boy suspended on silk cords, who was charged and attracted chaff, paper, etc, to his hands). He certainly realised that his phenomenon of 'electric virtue' was the same as lightning, many years before Franklin formulated his flying-kite theory.
When Sloane took over the Royal Society on Newton's death, Gray belatedly received the recognition denied him by the Newton faction. He was given the Society's first Copley Medal in 1731 for his work on conducation and insulation, and also its second in 1732 for the induction experiments. In 1732 he was also admitted as a member of the Royal Society, but he died destitute a few years later in 1736.
Despite the importance of his discoveries (you could well argue that he was the inventor of electrical communications) he received little credit at the time of his discoveries because of the factional dispute in the Royal Society, and the dominance of Newtonianism (which became the Masonic 'ideology'). By the time his discoveries were publicly recognised, experiments in electricity had moved rapidly on and his past discoveries tended to look trivial. For this reason, some historians tend to overlook his work.
There is no monument to Gray, and little recognition of what he achieved, against all odds, in his scientific discoveries. He is believed to be buried in a common grave in an old London cemetery, in an area reserved for pauper pensioners from the Charterhouse.