Dr Robert Dundas Thomson FRSE FRS FRCP FCS (21 September 1810 – 17 August 1864) was a British physician and chemist and a pioneer of public sanitation.
In his early career he applied chemical knowledge to the investigation of physiological question, including the composition of the blood, especially in cholera.
He was unsuccessful as a candidate for the chair at his uncle's death in 1852, but, returning to London, was appointed lecturer on chemistry at St. Thomas's Hospital on the retirement of Dr. Henry Beaumont Leeson.
He was elected a Fellow of the Royal Society of London on 1 June 1854 In 1856, when medical officers of health were appointed under the Metropolitan Local Management Act, Thomson was the successful candidate for Marylebone.
He became known as an authority on sanitary matters, and was employed by the registrar-general to make a monthly report of the amount of impurity in the supplies of the London water companies.