Between 25 million and 1 billion environmental migrants will move within and across borders by 2050, the majority of whom will be within Latin America, the Caribbean, South Asia and Sub-Saharan Africa. Relationships between climate change, migration, and health are heterogeneous. Migration, climate change and health are themselves complex systems with multiple drivers, dependent on the differential exposure, sensitivity, vulnerability, and adaptive capacity, and mediated by social, economic, political and demographic factors. As such, attempts to study the interface of these complex systems has proven challenging to quantify, predict and project; a reflection of the heterogeneity of the systems themselves. This paper aims to identify the research gaps and priorities within the nexus of these three complex systems, by: 1) reviewing the literature in the nexus of climate change, migration and health to summarise the identified research gaps and 2) surveying academics and practitioners who are part of the CliMigHealth (climate change, migration and health) International Thematic Network.