George Darell Maynard qualified as a Member of the Royal College of Surgeons of England (MRCS) and a Licentiate of the Royal College of Physicians of London (LRCP) in 1898. Three years later he became a Fellow of the Royal College of Surgeons of Edinburgh (FRCSE). He was licensed to practice in the Cape Colony on 14 June 1904. Soon thereafter he moved to the Transvaal, where he was registered in 1905. By 1907 he resided in Pretoria.
It seems that Maynard worked for the Department of Agriculture in Pretoria and published "Notes on experimental redwater inocculations", in the Transvaal Agricultural Journal (1906, Vol. 4, pp. 791-794). The author is identified as "G.A. Maynard, (FRCS)".
In due course Maynard settled in Johannesburg, where he was appointed as assistant medical officer of the Witwatersrand Native Labour Association. In this position he contributed a paper on "Aestival diarrhoeas of South Africa" to the Transvaal Medical Journal (1910/1, Vol. 6, pp. 26-33). He became known as a medical biometrician and published five papers in the journal Biometrika, dealing with statistical studies of anti-typhoid inoculation (1909), cancer death rates (1910), the age distribution of deaths from Diabetes Mellitus (1911), the distribution of cases of disease as determined by chance (1912), and human fertility (1923). He was the first author to propose statistical criteria of infectiousness.
In 1912 the South African Institute for Medical Research (SAIMR) was founded in the city through an agreement between the Government of the Union of South Africa and the mining industry, represented by the Witwatersrand Native Labour Association. Its primary purpose was to study human diseases in southern Africa. Maynard secured a research post at the Institute as statistician and pathologist, and that same year became the author of the first publication emanating from the Institute, a paper on "The relative importance of infection and heredity in the spread of tuberculosis", published in the Medical Journal of South Africa (October 1912). He hypothesized that the disease progressed faster in Blacks than in Whites, as the latter had probably been infected in childhood and were partly immune.
During his short stay at the Institute Maynard managed to write nine papers and reports, including "An inquiry into the aetiology, manifestations and prevention of pneumonia amongst natives on the Rand recruited from tropical areas", in the Institute's Publication No. 1 (1913, pp. 1-10), which was perhaps his most important contribution; Anthropological notes on Bantu natives from Portuguese East Africa (with G.A. Turner*, Johannesburg, 1914); and "The trypanosomes of sleeping sickness, being a study of the grounds for the alleged identity of T. brucei with those causing disease in man in Nyasaland" (SAIMR Publication No. 6, 1915). He played a leading role in pneumonia vaccination experiments during 1914, leading to a paper on "Pneumonia inoculation experiment No. 3" in the Medical Journal of South Africa (1915, Vol. 2, pp. 36-38). In a "Note on Drs Turner and Brebner's paper on serum treatment in cerebrospinal meningitis", in the August 1915 issue of the same journal, he questioned the efficacy of the treatment on the basis of a statistical and methodological analysis.
After leaving the Institute during World War I (1914-1918) Maynard served for more than two years with the Union Defence Force in East Africa and then remained with the South African Medical Corps, being posted first to Durban and later Pretoria. As a result of his contribution to the war he was appointed as an Officer of the Order of the British Empire in 1918. During 1919-1921 he published a number of notes on various diseases in the Medical Journal of South Africa. He became a member of the South African Association for the Advancement of Science in 1910. He died of cerebrospinal meningitis in 1923 and was survived by his wife, Monica Violet Maynard, born Erskine.