After qualifying from UCD, Johnston worked in the
Mater and
St James's hospitals in
Dublin, where he specialised in oncology and
hematology. In 1987, he took up a fellowship at the
National Cancer Institute at
Bethesda, Maryland, where he undertook doctoral studies in molecular pharmacology and was subsequently offered tenure in 1993. He began his career at Queen's in 1996, when he was appointed professor of oncology. Prior to his appointment as vice-chancellor, he was dean of the School of Medicine, Dentistry and Biomedical Sciences. In 2007, he led the development of a new international medical school at Queen's and the Institute of Health Sciences. Prior to this, he was the director of the Centre for Cancer Research and Cell Biology at the University. Johnston was made chair of the Translational Research Group of the
Medical Research Council (MRC) in 2012. He received the 2013 International Bob Pinedo Cancer Care Prize for his work in translating discovery science for the benefit of cancer patients. He served on the Cancer Research UK (CR-UK) Science Executive/Advisory Board and co-founded
Almac Diagnostics (based in
Craigavon) and the Society for Translational Oncology in
Durham, North Carolina. He was a fellow of the
Academy of Medical Sciences (appointed 2012) and the
National Cancer Institute (appointed 1987). He was made a senior investigator at the NCI in 1991. In 2012 he was awarded the
Diamond Jubilee Queen's Anniversary Prize, for his leadership at the University's Comprehensive Cancer Centre. After a reconsideration of the security and academic implications, the conference proceeded. ==Personal life==