Hermanus Johannes Steyn, ophthalmologist, qualified as Doctor of Medicine (MD) at the University of Amsterdam, The Netherlands, in 1916 with a thesis entitled Over de sametrekking van het nieuw gevormde bindweefsel in het oog: Een pathologies-anatomiese en kliniese studie (On the contraction of the newly formed connective tissue in the eye: A pathological-anatomical and clinical study; 280 p). He also at some time published a paper on 'Netvlies loslating' (retinal disattachment).
In 1924, back in South Africa, Steyn wrote a pamphlet entitled 'Ons nasionale strewe in Suidafrika' (Our national aspirations in South Africa), dedicated to General Herzog, founder of the National Party. He resided in Bloemfontein and by 1926 was honorary ophthalmic surgeon at the National Hospital, an executive member of the hospital board, and mayor of Bloemfontein. He resided in Bloemfontein until at least 1936 and was still active as an ophthalmic surgeon in 1941 [though it is not clear where].
Shortly before his death in 1966 Steyn was living in Windhoek and represented South West Africa (now Namibia) in the South African Senate. After the death of his first wife in 1936 he married Olga Dorothy Cameron. He had a son and two daughters.