Objective: In Canada and elsewhere, making treatment decisions for a person with serious mental illness (SMI) who was found incapable for treatment decisions via a substitute decision maker (SDM) is the norm. This practice is often called into question from a rights-based perspective. The literature on the views of affected individuals is limited. We explore the experiences of adults with SMI who have had SDMs to gain more in-depth understanding. Method: We conducted semistructured interviews with 11 consumers of psychiatric services who have had experiences with SDM (range 1–12 years) at an urban hospital in Toronto, Canada. Results: Thematic analysis showed five main themes and related subthemes, including: (1) strong dissatisfaction with and rejection of the SDM’s role and purpose; (2) pervasive sense of stigma associated with having a SDM; (3) ongoing struggles to gain autonomy; (4) mixed changes in relationship with and views about SDM; and (5) views on how to improve SDM process. Conclusion and Implications for Practice: Our study highlights substantial dissatisfaction with the current SDM system and approaches among adults with SMI who have had SDMs. Issues of stigma and struggles to regain autonomy are prevalent. We discuss the personal, clinical, and social-legal contexts in which they occur, particularly in light of the United Nations’ Convention on the Rights of Persons with Disabilities that calls for replacing SDMs with supported decision making. Rights-based approaches to care carry substantial practice implications and call for thoughtful change management.