Mason had hoped to continue research in the chemistry department, but his attempt to find a position was blocked by Robert Robinson as the result of a dispute between Robertson and Hammick.
In 1947 he was invited by F. Sherwood Taylor, the curator of the History of Science Museum, Oxford to join his staff as a departmental demonstrator (junior lecturer), on condition that he also became the secretary and treasurer of the Society for the Study of Alchemy and Early Chemistry.
His role in the museum was to give lectures of general interest on the history of science, which required greatly expanding his reading and knowledge.
He was offered a fellowship by Adrien Albert, the head of the Department of Medical Chemistry at the ANU, which was temporarily based in the Wellcome Institute in London.
In 1955 he had to move to UCL (his lab at the Wellcome was needed by the Institute), where he had the chance to improve his understanding of quantum chemistry and molecular spectroscopy.
On his retirement, Stephen Mason and his wife moved to Cambridge where, for the next couple of years he worked on his book Chemical evolution: origins of the elements, molecules and living systems,[6] supported by a Leverhulme Emeritus Fellowship.