Isaac Newton was born of English nationality on January 4, 1643, in Lincolnshire County, England.

At that time, the country is known today as Great Britain was not yet called as such, is then divided into the kingdoms of England (which included Wales) and Scotland, and therefore the phrase “of British nationality,” or “British citizen” could not have applied to Newton. 

However, after the enactment of the Treaty of Union in 1707, the Kingdom of England and the Kingdom of Scotland merged into one, creating the identity of the Kingdom of Great Britain. Accordingly, from this year on, Newton could be called a British national or British citizen.