The early part of his career was spent establishing and leading the Pharmacology and New Drug Development Laboratory at the Medical Research Council's Clinical Oncology Unit at the University of Cambridge, where he developed new treatments to exploit hypoxic cells in solid tumours and elucidated the enzymes involved in the activation of hypoxia-targeted drugs. In 1990 Workman spent a sabbatical period in the Department of Therapeutic Radiology, Stanford University and SRI International, California, USA where he continued his work on tumour hypoxia funded by a Fellowship from what was then the International Union Against Cancer. In 1991 Workman was appointed as a Cancer Research Campaign Life Fellow, Professor of Experimental Cancer Therapy, University of Glasgow and Director of Laboratory Research in the CRC Department of Medical Oncology, CRC Beatson Laboratories, Glasgow. Here he extended his research on tumour hypoxia and molecular targeted therapies. Workman also continued his service for the European Organisation for Research and Treatment of Cancer as Chairman of the EORTC Pharmacology and Molecular Mechanisms Group. Member of EORTC Board and Council as Chairman of the EORTC New Drug Development Coordinating Committee. Workman joined the ICR in 1997 to develop its Cancer Research UK Cancer Therapeutics Unit. Overall, since 2005, the Cancer Therapeutic Unit has discovered 17 drug candidates, seven of which have progressed to the patient trial stage. Workman has attributed this record to "taking early academic risks, combining academic and pharmaceutical expertise, and implementing strong leadership and project management. Other contributing factors include running multiple projects on a competitive scale, establishing long-term financial support and – most important – selecting productive and timely industrial collaborations." Workman was appointed Deputy CEO of the ICR in March 2011. Workman is currently working on drugs that block molecules essential for the growth and survival of cancer cells, in particular, molecular chaperones such as Hsp90. The leading Hsp90 inhibitor was discovered by Workman's team at ICR in collaboration with Vernalis.
