Critical Time Intervention (CTI) is designed to reduce the risk of homelessness and other adverse outcomes by providing support to individuals during challenging life course transitions. While several narrative reviews suggest the benefit of CTI, the evidence on the model's effectiveness has not been systematically reviewed. This article systematically reviews studies of CTI applied to a variety of populations and transition types. Following the Preferred Reporting Items for Systematic Review and Meta-Analysis for protocols (PRISMA-P) guidelines, we reviewed 13 eligible experimental and quasi-experimental studies. Findings were summarized by individual outcome domains, including housing, service engagement use, hospitalization or emergency services, mental health, substance use, family and social support, and quality of life. CTI had a consistent positive impact on two primary outcomes-reduced homelessness and increased service engagement use-among different populations and contexts. Despite the effectiveness of CTI, the specific mechanisms of the model's positive impacts remain unclear. Implications for practice, policy and research are addressed.