R. Fermor Rendell, only son of Henry Rendell, obtained the degree Bachelor of Arts (BA) at the University of London in 1894 and was elected a Fellow of the Royal Astronomical Society (FRAS) in 1896. From 1892 to 1903 he was employed on the staff of the Royal Greenwich Observatory, near London, and for some time during that period was assistant editor of the Journal of the British Astronomical Associaion. In March 1903 he accepted an appointment as senior astronomical assistant at the Natal Observatory, Durban, directed by E.N. Nevill*. He succeeded Mabel Nevill* in this post and assumed duty on 15 April. His duties were described by Nevill as follows: "The senior assistant maintains a general supervision over the whole of the details of the work of the Observatory; carries on the general and astronomical correspondence; assists when required in all observations made between eleven o'clock at night and eight o'clock the next morning; looks after, makes out, checks, and pays all accounts, keeping the necessary books, and preparing and rendering all the returns required by the Government; calculates all the ephererides, working lists, and tabular places; constructs all auxiliary tables and charts; reduces the magnetic observations and tidal records, and generally takes over the duties of the Junior and Meteorological Assistants when they are absent on leave or from illness" (Report of the Government Astronomer, 1903, p. 3).
Rendell produced some papers on both meteorological and astronomical topics during his stay in Natal. He became a member of the South African Association for the Advancement of Science and at the joint meeting of the British and South African Associations, held in South Africa in 1905, read a paper entitled, "Meteorological notes from Natal Observatory". It contained tables with monthly values of the rainfall, air pressure, maximum and minimum temperature, humidity, wind force, and cloudiness, observed at the observatory since 1884, and was included in the Addresses and papers... published after the meeting (Vol. 1, pp. 52-65).
During 1906 Rendell investigated the times of high water at Durban and prepared a table of improved predictions for 1906 and 1907. He also made a series of observations of Comet C of 1905, which were submitted to the Royal Astronomical Society for publication. Later that year he read two papers at the annual congress of the South African Association for the Advancement of Science held in Kimberley, one on "Recent cometary observations" (not published), the other "On predicting times of high water at Durban, Natal" (abstract published in the associaton's Report for 1906, p. 143). Also in 1906 a paper by him entitled "Rainfall at Durban, Natal" appeared in the Quarterly Journal of the Royal Meteorological Society. It contained monthly totals of rainfall for the period 1871 (when observations were started in the Natal Botanic Gardens where the Natal Observatory was later built) to 1905.
Rendell was admitted to the Bachelor of Arts (BA) degree by the University of the Cape of Good Hope in 1903, on the basis of his BA from the University of London. In 1906 he was an examiner in astronomy and trigonometry for the Certificate in the Theory of Surveying of the University of the Cape of Good Hope. He was not married, and served as a lay reader in the Church of England in Durban. He resigned his post at the Natal Observatory early in 1907 and left in March. The post remained vacant.