Keynes read Natural Sciences at Pembroke College, Cambridge, graduating MA in 1913. He went on to train as a doctor at St Bartholomew’s Hospital, London, and joined the Royal Army Medical Corps at the outbreak of the First World War. He returned to Bart’s as part of the surgical team after the war.

In his early career, Keynes was a pioneer in blood transfusion. He co-founded the London blood transfusion service with P. L. Oliver in 1921, and his Blood transfusion (London, 1922) was the first textbook on the subject to be published in Great Britain. He donated his collection of works concerned with the history of blood transfusion to the Royal College of Physicians, where he was Honorary Librarian, but the larger part of his library came to Cambridge in 1982.

References
Sir Geoffrey Keynes, The gates of memory (Oxford, 1981)
David McKitterick, ‘Keynes, Sir Geoffrey Langdon (1887–1982)’, rev. Stephen Lock, ODNB (Oxford, 2004)