John S. Marr was born in New York City and grew up in Manhattan. After graduating from Yale, he received an MD from New York Medical College. He then completed an MPH degree from the Harvard School of Public Health. After graduating, Marr was employed by the US Army's Academy of Health Sciences in San Antonio, Texas. His role was teaching about tropical disease to troops preparing to deploy to the Vietnam War. In 1974, Marr returned to New York as the city's principal epidemiologist, where he investigated a number of infectious disease outbreaks, including Legionnaires' disease. He went on to hold several private and government medical posts. His last post was as State Epidemiologist of Virginia, from which he retired in 2006.
