John M. Barry is a writer and historian, yet he has significant impact on public health in two distinct areas. In both instances, his role has grown out of his writing.

His book "Rising Tide: The Great Mississippi Flood of 1927 and How It Changed America" won the Francis Parkman Prize of the Society of American Historians for 1997's best book of American history. The book influenced views of flood protection, demonstrating the need for an integrated and comprehensives approach, the world, and that impact was recognized when the National Academy of Sciences invited him to become the first non-scientist to give the annual Abel Wolman Distinguished Lecture on Water Resources. Since Hurricane Katrina he has played a leading role in national and international flood protection. Immediately after the storm, the Louisiana Congressional delegation asked him to chair a bipartisan working group on flood control, and he has worked not only regionally and nationally but with the United Nations on flooding issues and preparedness, including in the public health sector. In 2007 a Democratic governor appointed him to two new government authorities, the Southeast Louisiana Flood Protection Authority East, which oversees several levee districts in the metropolitan New Orleans area, and the Louisiana Coastal Protection and Restoration Authority, which develops and implements the hurricane protection plan for the state. In 2009 a Republican governor reappointed him to both positions.

His second area of impact on public health has been on influenza pandemic preparedness, beginning with his book "The Great Influenza: The story of the deadliest pandemic in history." The National Academy of Sciences recognized this work with its 2005 Keck Award, given to the year's best book on medicine or science. More importantly, the book also helped energize efforts to prepare for a pandemic. According to several sources, it played a key role in convincing Congress to appropriate money for this purpose, Barry has also been directly involved in preparedness planning efforts. For this, the Center for Biodefense and Emerging Pathogens gave him its 2005 September 11th Award. He has advised both the Bush and Obama administrations and numerous state and local public health agencies, particularly in analyzing historical data that relates both to risk communication and non-pharmaceutical interventions. Currently he is Distinguished Scholar at the Center for Bioenvironmental Research of Tulane and Xavier Universities.