Objective This lived experience-engaged study aims to understand patient and family perspectives on the relationship between suicidality and medical assistance in dying when the sole underlying medical condition is mental illness (MAiD MI-SUMC). Method Thirty individuals with mental illness (age M = 41.8 years, SD = 14.2) and 25 family members (age M = 47.5 years, SD = 16.0) participated in qualitative interviews examining perspectives on MAiD MI-SUMC and its relationship with suicide. Audio recordings were transcribed and analysed using reflexive thematic analysis. People with lived experience were engaged in the research process as team members. Results Four main themes were developed, which were consistent across individuals with mental illness and family members: (a) deciding to die is an individual choice to end the ongoing intolerable suffering of people with mental illness; (b) MAiD MI-SUMC is the same as suicide because the end result is death, although suicide can be more impulsive; (c) MAiD MI-SUMC is a humane, dignified, safe, nonstigmatized alternative to suicide; and (4) suicidality should be considered when MAiD MI-SUMC is requested, but suicidality's role is multifaceted given its diverse manifestations. Conclusion For patient-oriented mental health policy and treatment, it is critical that the voices of people with lived experience be heard on the issue of MAiD MI-SUMC. Given the important intersections between MAiD MI-SUMC and suicidality and the context of suicide prevention, the role that suicidality should play in MAiD MI-SUMC is multifaceted. Future research and policy development are required to ensure that patient and family perspectives guide the development and implementation of MAiD MI-SUMC policy and practice.