His medical education was pursued at King's College Hospital, and whilst a student he took an active part in physiological investigations with Lionel Smith Beale.

in 1859, gaining the scholarship in medicine, a gold medal and honours in surgery, botany, and midwifery ; in 1860 he proceeded M.D.

In 1867 he was elected professor of physic at Gresham College, and lectured regularly and with increasing efficiency to the end of his life.

Symes-Thompson was specially interested in the value of climate and spa treatment for the relief of diseases, especially of the lungs, and travelled widely on the Continent, besides visiting Egypt, Algeria, and South Africa.

His most important contributions to medical literature were 'Lectures on Pulmonary Tuberculosis' (1863) and 'On Influenza: an Historical Survey' (1890), both being in part revision of books by his father.

He was also closely concerned in the publication by the Royal Medical and Chirurgical Society of the book entitled 'The Climates and Baths of Great Britain and Ireland’ (1895), besides contributing himself to its pages.

Life insurance also interested him greatly, and besides holding a prominent position amongst assurance medical officers in London as physician to the Equity and Law Life Assurance Society, he contributed an article on the subject to the two editions of Sir Clifford Allbutt's 'System of Medicine' (1896 and 1905).

In 1899 he bought Finmere House, Oxfordshire, where he spent much of his leisure and gratified an early love for botany and a country life.