Bill Stewart, is a plant physiologist and environmental microbiologist whose main research area is biological nitrogen fixation, particularly by cyanobacteria — an area in which he has published over 200 scientific papers.

He was founding Chair of Biological Sciences at the University of Dundee from 1967–1988. He served as Secretary of the Agricultural and Food Research Council (1988–1990), and Chief Scientific Adviser to the UK government and first Head of the Office of Science and Technology (1990–1995) during the restructuring of the research councils and the setting up of the Technology Foresight Programme. He was President of the Royal Society of Edinburgh, Scotland’s national academy of science and letters, from 1999–2002.

Bill also chaired the Independent Expert Group on the Decontamination of Gruinard Island of Anthrax, the Microbiological Research Authority, and the National Radiological Protection Board. He has served numerous biotechnology advisory boards, including SmithKline Beecham, Cyclacel (as Chair), and the BioIndustry Association (as President), and various environmental and public health committees, such as the Royal Commission on Environmental Pollution.