Medical assistance in dying (MAiD) was introduced into Canadian federal legislation in 2016. Mental illness as the sole underlying medical condition (MI-SUMC) is currently excluded from eligibility; such exclusion is scheduled to expire on March 17, 2024. Irremediability, capacity, quality of life, autonomy, family involvement, and healthcare system constraints have been debated intensively. Recent studies have not explored the views of family members of persons with mental illness on MAiD MI-SUMC. This study aimed to fill this knowledge gap. Twenty-five Ontario residents who had a loved one with mental illness participated. A persona–scenario exercise was designed to explore participants’ views on MAiD MI-SUMC in hypothetical situations. Reflexive thematic analysis was used to analyze the data. A lived experience-advisory panel was engaged throughout the study. Seven themes were developed: Witnessing suffering; A road with barriers and limitations; Societal barriers; The unknowns of mental illness; Individual choices: the life or death that a person wants; MAiD MI-SUMC as an acceptable choice when suffering cannot be relieved with available treatments and supports; and The emotional outcome. Participants constructed their views based on their experience of supporting a loved one with mental illness. MAiD MI-SUMC was perceived as a multifaceted issue, whose acceptability and potential introduction required a concurrent exploration and discussion of the challenges arising due to limitations of the healthcare system, the opportunities and limits to family involvement, and the value of patient autonomy.