Dr. Cassidy is a Senior Scientist in the Division of Health Care Outcomes and Research at the Toronto Western Research Institute, Director of the Centre for Research Expertise in Improved Disability Outcomes (CREIDO), Professor in the Division of Epidemiology at the Dalla Lana School of Public Health and cross appointed in Clinical Epidemiology in the Department of Health Policy, Management and Evaluation in the Faculty of Medicine at the University of Toronto. He also holds the Research Directorship in Artists' Health at the University Health Network.

Originally trained as a chiropractor, Dr. Cassidy practiced in both Ontario and Saskatchewan, where he was a member of the Medical-Dental Staff at the Royal University Hospital and a consultant chiropractor to the University of Saskatchewan's Student Health Centre. He also holds a Bachelor's degree in Anatomy, a Master of Science in Surgery and a Doctorate in Anatomical Pathology from the College of Medicine at the University of Saskatchewan. His second doctoral degree (Dr.Med.Sc.--Swedish Ph.D.) was earned in Epidemiology and Injury Prevention at Karolinska Institute in Stockholm, Sweden.

Dr. Cassidy has authored over 200 scientific papers and chapters in books, including publications in the New England Journal of Medicine, Achieves of Internal Medicine, Spine, and other international journals. His research interests include musculoskeletal and injury epidemiology. His current research focus is on disability prevention from occupational and traffic injuries and health issues in artists.