Persons with mental illness (PWMI) are often not afforded the same opportunity to make decisions on a par with others in society. Article 12 of the International Convention on the Rights of Persons with Disabilities (CRPD) states that persons with disabilities should have equal recognition before the law and the right to exercise their legal capacity. Exercising legal capacity can mean making decisions about employment, medical or psychosocial treatment, property, finances, family, and participation in community activities. The aim of this paper is to comprehensively review the evidence on supported decision making for PWMI, both in legislation and research globally, with a focus on low-and middle-income countries (LMICs). Results reveal only a few countries have provisions for supported decision-making for PWMI, with a particular shortage of such provisions in legislation in LMICs There is also a general paucity of research evidence for supported decision-making, with the majority of research focusing on shared decision-making for treatment decisions. This review highlights the need for additional research in this area to better guide models, which can be utilised in domestic legislation, particularly in LMICs, to better implement the ideals of Article 12 of the CRPD.