With over 80 million people forcibly displaced worldwide, providing safe, healthy, and supportive places for refugees has become an imperative for national governments, aid organizations, and host communities. While much has been written about the needs of these displaced people, organizations and practitioners tend to focus on essential material needs, medical care, and food and water provisioning. Yet a growing body of evidence points to the potential role of social capital - the bonding, bridging, and linking social ties that connect us to one another - as a critical resource for these refugees. We have little data about social capital interventions at individual and community levels to assist with mental health for this vulnerable population, and even less methodical evidence about such interventions' impact. This systematic review analyzes nearly 400 articles to find patterns in the literature on how social-capital-based interventions can improve the mental health of refugees. Within the studies of interventions that met our filtering criteria, the reinforcement or creation of social capital, especially bridging and linking types, serves as a crucial resource to help this vulnerable group. Specifically, our review showed that community and multilevel social capital interventions are key to curbing mental health symptoms among refugees. Given this scanty evidence base among a group so vulnerable to mental health problems, this review serves as an explicit invitation for researchers to further examine social capital interventions among refugees.