The purpose of this Review is to provide evidence for why gender equality in science, medicine, and global health matters for health and health-related outcomes. We present a high-level synthesis of global gender data, summarise progress towards gender equality in science, medicine, and global health, review the evidence for why gender equality in these fields matters in terms of health and social outcomes, and reflect on strategies to promote change. Notwithstanding the evolving landscape of global gender data, the overall pattern of gender equality for women in science, medicine, and global health is one of mixed gains and persistent challenges. Gender equality in science, medicine, and global health has the potential to lead to substantial health, social, and economic gains. Positioned within an evolving landscape of gender activism and evidence, our Review highlights missed and future opportunities, as well as the need to draw upon contemporary social movements to advance the field.