Barry has over 30 years of experience in applied epidemiology, perinatal epidemiology, and environmental epidemiology. He has published papers in these areas, developed, operated, and evaluated numerous health surveillance systems, conducted investigations of disease clusters, and teaches postgraduate courses in epidemiology. From 2000 to 2008, Barry managed Public Health Intelligence (PHI), the epidemiology group of the Ministry of Health, New Zealand, and previously was the senior epidemiologist in several government agencies. Since 1987, he has been the director of the New Zealand Birth Defects Registry (NZBDR), reporesenting New Zealand at the International Clearinghouse for Birth Defects Surveillance and Research (ICBDSR).
Barry is currently a member of 'The Ministry of Health Coronavirus Statistical Advisory Group'.