Despite a burgeoning of research on moral injury in the past decade, existing reviews have not explored the breadth of consequences and the multitude of pathways through which moral injury and potentially morally injurious experiences (PMIEs) influence mental and behavioural health outcomes. This study aimed to identify associations between moral injury on mental and behavioural health. Literature searches of psychological and medical databases were conducted through April 2020. Eligible studies measured moral injury or PMIEs, and health outcomes (e.g., depression, substance use and suicidality). Fifty-seven publications representing 49 separate samples were included. Studies examined the impact of moral injury on post-traumatic stress disorder (PTSD) (n = 43); depression (n = 32); anxiety (n = 15); suicide (n = 15); substance use (n = 14); and ‘other’ health outcomes, including pain, burnout, sleep disturbance and treatment-seeking behaviours (n = 11). The majority of studies found significant positive associations between moral injury-related constructs, mental health and behavioural health outcomes; however, the majority were also cross-sectional and focused on military samples. Proposed mediators included lack of social support, negative cognitions and meaning-making. Moderators included self-compassion, pre-deployment mental health education and mindfulness. Moral injury is associated with a variety of negative health outcomes. Research is needed to determine the mechanisms by which moral injury may influence these outcomes over time.