In 2015, the United Nations Sustainable Development Goals (SDGs) set the course for a more equitable distribution of resources globally. For the first time in history, this collective global commitment explicitly included mental health-related objectives, and manifested them as targets in the health SDG 3. This represents a unique opportunity to increase coverage and quality of services, especially in low- and middle-income countries, in which the current treatment gap surpasses 80% even for the most severe disorders. Importantly, although not explicitly highlighted in the SDGs, mental health is implicitly cross-linked to multiple of the other goals and targets, which stresses the importance of investing in improving population-level mental health as a pre-condition to: ending hunger, achieving food security and improved nutrition, and promoting sustainable agriculture (SDG 2); ensuring inclusive and equitable quality education and promoting life-long learning opportunities for all (SDG 4); promoting sustained, inclusive and sustainable economic growth (SDG 8); reducing inequality within and among countries (SDG 10); making cities and human settlements inclusive, safe, resilient and sustainable (SDG 11); promoting peaceful and inclusive societies (SDG 16); and, obviously, ensuring healthy lives and promoting well-being for all at all ages (SDG 3). In this article, we revise the reasons why investing in, and improving, mental health systems and services, constitutes a fundamental step towards achieving the overall SDGs, and we highlight the role that civil society, NGOs, and academic organizations need to play to ensure that these commitments are fulfilled.