Ellis became scientific officer in the ARC (Agriculture Research Council) Unit of Plant Physiology,
Imperial College,
University of London, 1959–61 and an ARC Research Fellow at the Department of Biochemistry,
University of Oxford, 1961–64, working on the regulation of bacterial sulphate reduction with Professor C. A. Pasternak. In 1964, Ellis joined the
University of Aberdeen as a lecturer in the Department of Botany, and moved to its Department of Biochemistry in 1968, following a visiting professorship in the
University of Toronto in 1967. In 1970, Ellis moved to the newly created Department of Biological Sciences,
University of Warwick, as senior lecturer and founding head of the
Chloroplast Research Group. Ellis has remained at Warwick University as reader (1973), holder of a personal chair (1976), and emeritus professor (1996). He was a visiting professor at the Department of Chemistry,
University of Oxford from 1996 until 2000. From 1990 until 2009, he organised annual meetings of the UK Molecular Chaperone Club at the Universities of Oxford, Cambridge, London, Bristol, Birmingham and Warwick. Ellis is the author of
How Science Works: Evolution. == Principal research achievements ==