The ongoing COVID-19 pandemic is a devastating global health crisis. Without a vaccine or effective medication, the best hope for mitigating virus transmission is collective behavior change and support for public health interventions (e.g., physical distancing, physical hygiene, and endorsement of health policies). In a large-scale international collaboration (N = 46,450 across 67 countries), we investigated why people adopted public health behaviors and endorsed public policy interventions (e.g., closing bars and restaurants) during the early stages of the pandemic (April-May, 2020). Results revealed that respondents who identified more strongly with their nation consistently reported engagement in public health behaviors and greater support for public health policies. We also found a small effect of political orientation, indicating that left-wing respondents were more likely to report public health behaviors and support for public health measures than right-wing respondents. We discuss the implications of links between national identity, leadership, and public health for managing the COVID-19 pandemic and future pandemics.