Poynter made a number of important contributions to the study of the history of medicine and his influence was felt throughout the world.
He was a prime mover in the founding of the Faculty of the History of Medicine of the Society of Apothecaries in 1958.
He was an active member of the Société Internationale d’Histoire de la Médecine, contributing to its reorganisation.
His links with American historians led to his appointment to the editorial board of the Journal of the History of Medicine and Allied Sciences.
Poynter was a regular contributor to journals and author of a series of books, many of which dealt with medicine in Tudor and Stuart times.