Background: The coronavirus (COVID-19) pandemic has seen a global surge in anxiety, depression, post-traumatic stress disorder (PTSD), and stress. Aims: This study aimed to describe the perspectives of patients with COVID-19, their family, health professionals, and the general public on the impact of COVID-19 on mental health. Methods: A secondary thematic analysis was conducted using data from the COVID-19 COS project. We extracted data on the perceived causes and impact of COVID-19 on mental health from an international survey and seven online consensus workshops. Results: We identified four themes (with subthemes in parenthesis): anxiety amidst uncertainty (always on high alert, ebb and flow of recovery); anguish of a threatened future (intense frustration of a changed normality, facing loss of livelihood, trauma of ventilation, a troubling prognosis, confronting death); bearing responsibility for transmission (fear of spreading COVID-19 in public; overwhelming guilt of infecting a loved one); and suffering in isolation (severe solitude of quarantine, sick and alone, separation exacerbating grief). Conclusion: We found that the unpredictability of COVID-19, the fear of long-term health consequences, burden of guilt, and suffering in isolation profoundly impacted mental health. Clinical and public health interventions are needed to manage the psychological consequences arising from this pandemic.