Clinical applications of biomedical research rely on specialist knowledge provided by professionals who straddle research and therapy, and possess both medical and scientific expertise. To date, this professional group remains under-explored in sociology. Our article presents a case study of clinician-scientists working in stem cell research for heart repair in the UK and Germany who are engaged in double-blind randomised clinical trials using patients’ own stem cells. The analysis draws on sociological and medical literature, interviews and ethnographic fieldwork to analyse the experiences and self-rationalisations of a small number of clinician-scientists and the ways in which these professionals portray, explain and justify their role in the wider clinical research environment. We examine our participants’ views on the clinical trials they conduct, the challenges they encounter and the ways through which they negotiate a complex disciplinary terrain, and argue that the recent clinical implementation of stem cell research brings clinician-scientists to the fore and provides a renewed platform for their professional legitimisation. The article helps increase our understanding of how randomised clinical trials are involved in consolidating the individual status of actors and the collective standing of clinician-scientists as leaders of change in translational medicine.