Richard Keynes was born on 14 August 1919, the eldest son of Sir Geoffrey Keynes, MD, FRCP, FRCS, FRCOG, and Margaret Elizabeth, daughter of Sir George Darwin, KCB. He was educated at Oundle School (as a Scholar) and then Trinity College, Cambridge (again as a Scholar). In 1945 he married Anne Pinsent Adrian, eldest daughter of 1st Baron Adrian, OM, FRS, and Dame Hester Agnes Adrian, DBE, only daughter of Hume C. and Dame Ellen Pinsent, DBE; they had three sons (and one son deceased).

During the war, Keynes served as a temporary experimental officer at the Anti-Submarine Establishment and Admiralty Signals Establishment (1940-45), returning to Cambridge after the war to complete his degree (1st Class, Natural Science Tripos Part II, 1946). Keynes remained at Trinity College as a Research Fellow between 1948 and 1952, winning the Gedge Prize in 1948 and the Rolleston Memorial Prize in 1950. His career at Cambridge included: demonstrator in Physiology (1949-53); Lecturer (1953-60); Fellow of Peterhouse College (1952-60, and an Honorary Fellow, 1989); Head of the Physiology Department, and first Deputy Director (1960-64), then Director (1965-73); Director of the ARC Institute of Animal Physiology (1965-72); Professor of Physiology (1973-87); Fellow of Churchill College, since 1961.

Outside Cambridge, Keynes's positions included: Secretary-General of the International Union for Pure and Applied Biophysics (1972-78), then Vice-President (1978-81) and President (1981-84); chairman of the International Cell Research Organisation (1981-83) and the ICSU/Unesco International Biosciences Networks (1982-93); President of the European Federation of Physiological Societies (1991); a Vice-President of the Royal Society (1965-68); Croonian Lecturer (1983); Fellow of Eton College (1963-78); foreign member of the Royal Danish Academy (1971), American Philosophical Society (1977), American Academy of Arts and Sciences (1978) and the American Physiological Society (1994).

Keynes's publications include: The Beagle Record (1979); (with D. J. Aidley) Nerve and Muscle (1981, 2nd edition 1991); he edited the Beagle Diary of his great-grandfather, Charles Darwin (1988); edited jointly Lydia and Maynard: the letters of Lydia Lopokova and John Maynard Keynes (1989); papers in the Journal of Physiology, Proceedings of the Royal Society etc.

Keynes's honours and awards include: CBE (1984); MA, PhD, ScD Cantab; FRS (1959). He died on 12 June 2010.