BackgroundThe COVID-19 pandemic has presented many countries with significant health system and economic challenges. The role of civil–military cooperation in a health crisis of the magnitude presented by COVID-19 remains virtually unexplored. This review aims to detect and identify typologies, if any, of associations between security or military systems and the national response measures during the COVID-19, as adopted by six European countries during the early phase of the outbreak (January to March 2020).MethodsWe designed a structured qualitative literature review (qualitative evidence synthesis), primarily targeting open-source grey literature using a customised Google web search. Our target countries were UK, France, Spain, Italy, Belgium and Sweden. We employed a ‘best fit’ framework synthesis approach in qualitative analysis of the result records.ResultsA total of 277 result records were included in our qualitative synthesis, with an overall search relevance yield of 46%. We identified 19 distinct descriptive categories of civil–military cooperation extending across seven analytical themes. Most prominent themes included how military support was incorporated in the national COVID-19 response, including support to national health systems, military repatriation and evacuation, and support to wider public systems.ConclusionFindings of this review show the significance of military systems in supporting an expansive response during the COVID-19 pandemic, and our proposed methodological approach for capturing military health data in a reproducible manner and providing a comparative view on common types of interventions provided by civil–military cooperation to inform lessons from the use of military capacities during current COVID-19 outbreak.