Distinguished surveyor, cartographer, mathematician and antiquary.

Little is known of Roy's early career. He first came to prominence in 1746 when King George II of England charged him with producing a survey of Scotland which would enable more effective policing of the country. From 1747 to 1755 Roy worked on a detailed hand-drawn map.

From 1783/74 Roy conducted observations for determining the relative positions of the royal observatories in Greenwich, England and Paris, France. He completed an extremely elaborate and accurate set of mathematical experiments and observations in order to determine the true and exact latitude and longitude of the two observatories. This work was to form the basis of all subsequent surveys.

Roy was commended for the accuracy of his work and in 1785 won the Copley medal of the Royal Society of London. His vision was to create an organisation responsible for mapping and surveying the whole of Britain but the Ordnance Survey was not founded until a year after his death.

Roy was also a noted antiquarian, studying Roman remains. His Military Antiquities of the Romans in Scotland was published in 1793.