Fothergill was born at Carr End, near Bainbridge in Yorkshire, the son of John Fothergill (1676-1745), a Quaker preacher and farmer, and his first wife, Margaret Hough (1677-1719).
Fothergill's pamphlet, Account of the Sore Throat attended with Ulcers (1748), contains one of the first descriptions of streptococcal sore throat in English, and was translated into several languages.