In a global pandemic, public health outcomes are not the only variables at stake. Also at stake are countries’ nation brands and influence, which hinge on how a country responded to the crisis. Based on a case study of a middle power, South Korea, one of the more successful COVID-19 national responses so far, we offer an exploratory conceptual explication of pandemic public diplomacy that is grounded in a normative framework of substance, information, trust, collaboration, and mutual benefit. Sentiment analyses of social media and international news media suggest that the country is perceived as a model on how to cope with the pandemic by international audiences. Unlike other public diplomacy contexts, pandemic public diplomacy challenge conventional assumptions about public diplomacy and nation branding. As nation-states confront a common enemy, how public diplomacy and nation branding play out in COVID-19—arguably the most socially disruptive event in modern history—helps to shed light on the dynamics of mutual interdependence in an interconnected yet competitive world fraught with fear, uncertainty, and information deficiency.