There is a global need to provide human resources for health in low- and middle-income countries. To increase access to care, task shifting has been implemented in community-based rehabilitation (CBR) programs where skills and responsibilities are transferred to local people with shorter and more focused training. Through realist review and synthesis, this research aimed to consolidate the literature when considering (a) what skills CBR workers are reportedly using and/or being trained in relating to mental health, (b) how different settings affect how these task shifting programs work, and (c) the evidence of effectiveness when community health workers come from within the community itself. A total of 11 databases (PubMed, ABI/Inform Global, CINAHL, Cochrane, Emerald, Google Scholar, PsycINFO, SAGE, Science Direct, Scopus, and Web of Science) were systematically searched for specific terms relating to mental health, CBR, and low- and middle-income country. A total of 27 publications were identified as fitting the criteria (4 qualitative, 20 quantitative including 10 randomized controlled trials, and 3 noninvestigatory editorials). Core skills have been identified along with themes that affect how programs work in particular contexts. The use of task shifting in this area may be a potentially viable option for increasing access to mental health care. This resulted in the development of a theory to explain the outcomes being observed. When Task-shifting mental health intervention skills collaboration, harnessing resources available within the community, and the provision of ongoing supervision interact to influence awareness gains, social bonding, the building of trust, and the development of skills and understanding within the community itself. This effects intervention buy-in, overall effectiveness and sustainability, mental health symptoms and local empowerment. These findings can be considered when developing training programs for CBR mental health workers, as well as policy and intervention program design.