Mental health is increasingly recognised as a global health priority, with 'global mental health' gaining relevance as a field. We thus aimed to identify the most influential actors in global mental health and key challenges in the design and implementation of policies and interventions within this relatively nascent field, to provide suggestions on how mental health could be promoted and diversified at the global level to improve mental health outcomes. We conducted a mixed-methods study, incorporating a social network analysis of 115 experts to identify the most influential mental health actors and elements globally and 30 semi-structured key informant interviews, analysed thematically, to examine key challenges in developing the field. We found concentrated influence among a few actors, with network analysis highlighting psychiatry followed by psychology as most influential specialties, and academia as the most influential sector; limited global collaboration and political engagement; and the need for greater professional, socio-cultural, geographical, and gender diversity. Sustaining mental health prioritisation globally requires directed and coordinated efforts from influential individual and institutional actors in the global mental health field. This requires critical engagement with dominant modes of knowledge production, greater synergy at global, national, and community levels, and agenda setting by a broader and more equitable coalition of global mental health actors across professional, cultural, and gender differences.