Can a human right to good mental health be justified? This is an under-explored question: until recently, rights in relation to mental health have been framed and debated primarily in terms of their relevance to psychosocial disability and mental ill-health/mental distress. By contrast, in this article, I propose the basis of a normative justification for a population-wide right to good mental health, focusing in particular on individuals who do not experience mental ill-health/distress or do not have (or may never have) a psychiatric diagnosis or a psychosocial disability. The article is structured into three parts. First, I will outline the emergence of a population-wide right to good mental health in mental health discourse, led by recent reports published by the former United Nations Special Rapporteur on the Right to Health, Danius Pūras. I will then go on to explore what we might understand by 'good mental health'. Finally, I will explain how a right to good mental health may be justified, drawing on insights from compassion, 'vulnerable agency', and James Wilson's account of 'a right to public health'. I then respond to feasibility and demandingness concerns about such a right, which together inform the basis of the qualified public health right to good mental health I propose.