She was born 1 September 1923 in Hampstead, London. Her parents were David M. S. Watson FRS, a vertebrate paleontologist and professor of zoology and comparative anatomy in the University of London, and Katharine M. Parker, who did research in embryology before marrying. Watson grew up with her sister Katharine Mary in South Hampstead and attended the local school, before going to Reading University to read General Science. She graduated with a first class honours degree in biology and geology in 1943.
After graduation, she tried working at the National Institute for Research in Dairying looking at chicken growth and later teaching biology at Wentworth School, Bournemouth before deciding to become a geologist. She applied to Imperial College in 1945, completing her BSc in Geology in 1947, again getting a first class degree. After her second graduation, the then head of department, Herbert Harold Read, took her on as his student and set her to work on the migmatites of Sutherland. She then began to work on the Lewisian complex of NW Scotland together with John Sutton, another of Read's research students. The two completed their PhD theses in 1949 followed by a wedding and honeymoon in the Channel Islands, which explains a joint publication on the geology of Sark a few years later.
After the award of their PhDs, they both joined the staff at Imperial College. They published their thesis work in a paper in 1951, that had a major impact on the study of Precambrian basement complexes, by showing that it was possible to understand their metamorphic and structural development as a series of discrete orogenic events that could be discerned in the field. They proposed that an older Archaean Scourian complex, had been partially reworked by a younger paleoproterozoic Laxfordian orogenic event, as shown by its effect on a set of dolerite dykes, known as the Scourie dykes. Subsequent fieldwork, metamorphic studies and radiometric dating has refined their chronology but supported their original hypothesis.
They continued to work together on other aspects of the precambrian geology of Scotland, including the Moine, Dalradian and Torridonian. John Sutton became head of department at Imperial College in 1964 and from then on their joint publications became less frequent. Watson published an introductory textbook Beginning geology with her former PhD supervisor H.H.Read in 1966, followed by Introduction to Geology: Volume 1 Principles in 1968 and Introduction to geology Volume2 Earth history: Part 1 Early Stages of Earth History and Part 2 Later Stages of Earth History in 1975.
In 1975 Watson was appointed to a personal chair as research professor of geology. She continued to work on the problems of the precambrian in Scotland but also published on ore genesis and regional geochemistry. She served as president of the Geological Society from 1982–1984, the first woman to hold that post.
- Lyell Fund - awarded jointly with John Sutton 1954
- Bigsby Medal - awarded jointly with John Sutton 1965
- Lyell Medal - awarded 1973
- Clough Medal - awarded 1979
- Royal Society - elected as fellow 1979, member of the council and vice-president until her death
- Fettes, D. J.; Plant, J. A. (1995). "Janet Watson. 1 September 1923-29 March 1985". Biographical Memoirs of Fellows of the Royal Society. 41: 500. doi:10.1098/rsbm.1995.0030.
- Ogilvie, M.B.; Harvey J.D. (2000). The Biographical Dictionary of Women in Science:L-Z. Taylor & Francis. pp. 1350–1351. ISBN 978-0-415-92040-7. Retrieved 2010-02-13.
- Geological Society, London (1994). "Catalogue of the papers and correspondence of JANET VIDA WATSON FRS (1923 - 1985)". Retrieved 13 February 2010.
- Bowes, D.R. (1987). Janet Watson—an appreciation and bibliography (PDF). Special Publications. 27. Geological Society, London. pp. 1–5. doi:10.1144/GSL.SP.1987.027.01.01. Retrieved 2010-02-13.
- Imperial College (2007). "A celebration of Earth Science and Engineering at Imperial College London 1907-2007" (PDF). p. 20. Retrieved 13 February 2010.
- Sutton, J.; Watson J (1951). "The pre-Torridonian metamorphic history of the Loch Torridon and Scourie areas in the north-west Highlands, and its bearing on the chronological classification of the Lewisian.". Quarterly Journal of the Geological Society, London. 106: 241–307. doi:10.1144/GSL.JGS.1950.106.01-04.16.
- Park, R.G.; Stewart A.D.; Wright D.T. (2002). "3: The Hebridean terrane". In Trewin N.H. The geology of Scotland. Geological Society, London. pp. 45–80. ISBN 978-1-86239-126-0. Retrieved 2010-02-13.