Lifestyle physical activity (LPA) interventions are a promising alternative to structured exercise interventions for addressing mental health problems. The authors conducted a systematic review of the literature on LPA interventions in any population in order to determine (a) the extent to which mental health outcomes were examined and (b) whether benefits in mental health outcomes were observed. Mental health outcomes were defined as depression, anxiety, perceived stress, health-related quality of life, and psychological well-being. A total of 73 articles were identified as LPA intervention, of which 24.7% (n = 18) reported the effect of LPA intervention on mental health outcomes. The most commonly evaluated mental health outcome was depression, and to a lesser extent anxiety and perceived stress. Overall, findings point to promising effects of LPA interventions across common mental health problems. Key areas for future research are discussed in light of emergent limitations in existing published studies.