Background: Supporting the decision-making of mental health service users fulfils professional, ethical and moral obligations of mental health practitioners. It may also aid personal recovery. Previous research on the effectiveness of supported decision-making interventions is limited. Aims: The study aims to explore from several perspectives the barriers and facilitators to supported decision-making in an Australian context. Supported decision-making was considered in terms of interpersonal experiences and legal supported decision-making mechanisms. Methods: In all, 90 narrative interviews about experiences of supported decision-making were conducted and analysed. Participants were mental health service users who reported diagnoses of schizophrenia, psychosis, bipolar disorder and severe depression; family members supporting them and mental health practitioners, including psychiatrists. The data were analysed thematically across all participants. Results: Negative interpersonal experiences in the mental health care system undermined involvement in decision-making for people with psychiatric diagnoses and family carers. Mental health practitioners noted their own disempowerment in service systems as barriers to good supported decision-making practices. All groups noted the influence of prevailing attitudes towards mental health service users and the associated stigma and discrimination that exist in services and the broader community. They believed that legal supported decision-making mechanisms facilitate the participation of mental health service user and their family supporters in supported decision-making. Conclusions: Enabling supported decision-making in clinical practice and policy can be facilitated by (1) support for good communication skills and related attitudes and practices among mental health practitioners and removing barriers to their good practice in health and social services and (2) introducing legal supported decision-making mechanisms.