He married Sarah Winstedt, a physician and surgeon with the Colonial Medical Service whom he had met in Kuala Pilah, in 1921.
He returned to England and was appointed Lecturer, then Reader, and ultimately Honorary Fellow, in Malay at the School of Oriental Studies in London, where he also served as a member of the Governing Body, 1939–1959.
Winstedt served on numerous boards and advisory groups, most notably at the Royal Asiatic Society in London, of which he was repeatedly the president and a Gold Medallist in 1947.
Other organisations included the Association of British Malaya, of which he was president in 1938, the Colonial Office Advisory Committee on Education, 1936–1939, and the Royal India Society.
He was a Fellow of the British Academy, an Honorary Member of the Southeast Asia Institute, the Royal Batavian Society, and the Koninklijk Instituut voor Taal-, Land- en Volkenkunde.