PurposeConcerns have been raised regarding the mental health of firefighters. In response to this, existing literature reviews have highlighted the significant role of trauma in influencing mental health and the experience of post-traumatic stress within firefighters.Design/methodology/approachThis paper builds on the existing reviews and makes an original contribution to knowledge by systematically reviewing research exploring additional factors that contribute to poor mental health in firefighters.FindingsThis review finds that factors such as sleep, occupational stress, length of service, coping style and social support all influence negative mental health within firefighters. However, this paper also suggests there are challenges to distinguishing the nature of these relationships, due to the possible bidirectional nature of the relationships and study limitations.Originality/valueFinally, we conclude by suggesting a clear need for further research to explore the biological, psychological and social factors influencing mental health outcomes in firefighters and the direction of these relationships, in order to inform effective intervention and support.