The aim of this study was to understand how policy actions implemented by city governments to improve infrastructure within the built environment can in turn influence healthy behaviors and population health. The authors investigated the associations between policy actions implemented by city governments to improve biking infrastructure and multiple health outcomes including leisure-time physical inactivity, obesity and coronary heart disease (CHD). In addition, this study tested if bike use for commuting and leisure-time physical activity were mediators between policy actions to improve biking infrastructure and health outcomes, and whether the health effects of bike infrastructure were different in cities of different population density. We merged local sustainability survey data with city-level chronic disease measures for the largest cities in the U.S. (n = 457). Results from regressions using Ordinary Least Squares estimation and mediation tests showed policies implemented to improve biking infrastructure were associated with lower prevalence of leisure-time physical inactivity, obesity and CHD. These relationships were most notable in medium-density cities (1,500-3,000/sq. mi). Moreover, leisure-time physical activity and active commuting mediated the relationship between bike infrastructure improvement policies and health outcomes. This study demonstrated the value of a policy-based intervention in enhancing population health. © 2024 Urban Affairs Association.