Aim: To summarise commonalities and variations in the mental health response to COVID-19 across different sites and countries, with a view to better understanding key steps not only in crisis management, but for future systemic reform of mental health care. Method: We conducted a Rapid Synthesis and Translation Process of lessons learned from an international panel of experts, collecting on the ground experiences of the pandemic as it evolved in real time. Digital conferencing and individual interviews were used to rapidly acquire knowledge on the COVID-19 outbreak across 16 locations in Australia, Denmark, Italy, Spain, Taiwan, the UK, and the USA. Results: COVID-19 has had massive impacts on mental health care internationally. Most systems were under-resourced and under-prepared, struggling to manage both existing and new clients. There were significant differences between sites, depending on the explosivity the pandemic and the readiness of the mental health system. Integrated, community mental health systems exhibited greater adaptability in contrast to services which depended on face-to-face and hospital-based care. COVID-19 has demonstrated the need for a new approach to rapid response to crisis in mental health. New decision support system tools are necessary to ensure local decision-makers can effectively respond to the enormous practical challenges posed in these circumstances. Conclusions: The process we have undertaken has generated clear lessons for mental health policymakers worldwide, beyond pandemic planning and response to guide next steps in systemic mental health reform. Key here is achieving some balance between national leadership and local context adaptation of evidence.