Indigenous children living in high income countries such as Australia, New Zealand, Canada and the United States of America (USA) are disproportionately affected by mental health problems when compared to their non-Indigenous counterparts. Childhood mental health disorders such as anxiety, depression and externalising behaviours are associated with a range of negative outcomes that are overrepresented in Indigenous communities, including high rates of suicidal ideation and completed suicide. The long-term sequelae of poor childhood mental health is believed to significantly contribute to the many health and social ‘gaps’ between Indigenous and non-Indigenous populations that occur throughout the lifespan. This systematic review of published evidence aimed to identify modifiable psychosocial risk and protective factors, common to Indigenous children living in developed countries that are associated with mental health outcomes typically associated with school-aged children. The results may inform policy and aid the design of initiatives to improve the mental health of Indigenous children, as well as identifying areas for further research.