DMS Watson was born at Higher Broughton, near Salford, Lancashire, only son of the two children of David Watson, chemist, metallurgist, and pioneer of the electrolytic refining of copper, and his wife Mary, daughter of Samuel Seares, a London stockbroker, 1886. He was educated privately and at Manchester Grammar School and entered the University of Manchester in 1904. He intended a career in chemistry and industry, but in fact specialised in geology, and while an undergraduate began to study preserved plants from Coal Measures deposits, producing a seminal paper with Marie Stopes on coal balls in 'Philosophical Transactions', vol 200B, 1907.
Watson was appointed Beyer fellow at the University of Manchester in 1908 and became interested in fossil reptiles and other vertebrates, visited many fossil localities in Britain, and worked intensively in the British Museum (Natural History) (BMNH), 1908-1911. He became interested in the BMNH collection of fossil reptiles from the Karoo (Karroo) of South Africa, and to further his knowledge collected extensively there, met the palaeontologist Robert Broom, and set up a subdivision of the Beaufort Series into biostratigraphical zones in 1911. That year he was invited by James P Hill to be honorary lecturer in vertebrate palaeontology at University College London, and was Lecturer in Vertebrate Palaeontology, University College London from 1912-1921.
He travelled to Australia and North America in 1914-1916, returning to Britain and taking a technical commission as lieutenant in the Royal Naval Volunteer Reserve from 1916-1918, transferring to the Royal Air Force as a captain, working on airship and balloon fabrics in 1918. After World War One, he conducted research at Newcastle upon Tyne on coal measure amphibia and fish and returned to University College London in 1920, succeeding A V Hill as Jodrell Professor of Zoology and Comparative Anatomy in 1921.
During WWII, Watson supervised the evacuation of the department to Bangor before becaming Secretary of the Scientific Subcommittee of the Food Policy Committee of the War Cabinet in 1940. In 1945 he returned to University College in Bangor and, when the war-damaged department was made habitable, in London. He remained at UCL until he retired from his chair and became Emeritus Professor in 1951, then was appointed Alexander Agassiz visiting professor at Museum of Comparative Zoology, Harvard, 1952-1953. However, he continued to have the use of a room at UCL and with his secretary and illustrator since 1928, Joyce Townsend, continued to write papers until his full retirement from scientific research in 1965.
In 1917 he married Katharine Margarite Parker and they had two daughters, Katharine Mary and Janet Vida. D M S Watson died in 1973. See also F R Parrington and T S Westoll's memoir in 'Biographical Memoirs of Fellows of the Royal Society', vol xx (1974), pp 483-504.