We conducted a large-scale survey covering 58 countries (N = 108,075) at the onset of the COVID-19 pandemic—between March 20th and April 7th 2020—to explore how beliefs about citizens’ and government’s response to the COVID-19 pandemic, and the actions taken by governments, affected mental well-being. Our analyses reveal three findings. First, many respondents indicate that their country’s citizens and government’s response was insufficient. Second, respondents’ perception of an insufficient public and government response was associated with lower mental well-being. Third, we exploit time variation in country-level lockdown announcements, both around the world and through an event-study in the UK, and find that strong government actions—i.e., announcing a nationwide lockdown—were related to an improvement in respondents’ views of their fellow citizens and government, and to better mental well-being. These findings suggest that policy-makers may not only need to consider how their decisions affect the spread of COVID-19, but also how such choices influence the mental well-being of their population.