Dr. Barr was born in Scotland and attended the University of Glasgow where he graduated from the Faculty of Medicine (MB, ChB with commendation) in 1966. After training in internal medicine and hematology, he spent two years at the University of Nairobi (Kenya) where he helped establish the Faculty of Medicine. There he began his involvement in the care of children with blood diseases and cancer.

After two years as a Visiting Scientist at the National Cancer Institute in the USA, and a brief return to Scotland where his research earned him the degree of MD with honours, Dr. Barr joined the Department of Pediatrics at McMaster University in 1977. He is currently a Professor in the Departments of Pediatrics, Pathology and Medicine, and completed 30 years as the Chief of Hematology-Oncology at McMaster Children's Hospital.

Dr. Barr's area of investigative activity is outcomes research in pediatric hematology-oncology, particularly in the measurement of health status and health-related quality of life, and in the adverse effects of cancer treatment on bone health. He has published more than 250 scientific articles and has written and contributed to several books on cancer in childhood and adolescence.

Dr. Barr's long-standing involvement in international health is reflected in his membership of the International Network of Cancer Treatment and Research, based in Brussels, and in his continuing work with a consortium of colleagues in Central America. He is an Honorary Fellow of the Royal College of Pediatrics and Child Health in the United Kingdom and a Fellow by election of the Royal Colleges of Physicians in Glasgow, London and Canada; the American College of Physicians and the Royal College of Pathologists.