Born in 1942, Thomas received his education at Norwich School before attending Cambridge (MA, 1964) and completing a PhD (1967, King's College London with John Randall) studying the diversity of protists with the recently-developed electron microscope.  

After this, he worked in Rockefeller University (1967-9), then returned to KCL as a Lecturer where he developed and tested numerous theories on the evolutionary history of life and taxonomy. He worked on chromosomes, centrosomes and cilia and what they could tell about the evolution of eukaryotes.  He was promoted to Reader in 1982 before taking up Professorship in Botany at the University of British Columbia in 1989 and the Chair in Evolutionary Biology at the University of Oxford in 2000. His repeated re-classification of the Kingdoms of Life catalysed debate and progress in evolutionary biology. He died in 2021