[4] He won scholarships from his school and universities that covered most of the cost of his education and his move from Cambridge to London was prompted by a vacancy for a salaried position as an assistant in the Botanical Department of the British Museum.
He was Keeper of Botany at the Natural History Museum from 1906 to 1930, in succession to George Robert Milne Murray.
This long gap was attributed by Rendle to his "increasing official and non-official duties".
These included acting as botany editor for the Encyclopædia Britannica Eleventh Edition, published in 1911, editor of the Journal of Botany (1924–1938), and revising the 7th edition Handbook of British Flora (1924, author G. Bentham).
His contemporaries considered that he had a keen sense of duty which he brought to his roles at the British Museum and contribution to the scientific community.