An abundance of modelled evidence attests to the health co-benefits of climate mitigation action across many sectors of society. Increased ambition is urgently needed to accelerate progress and achieve the health co-benefits from a just transition to a net-zero emissions future. Health co-benefits are additional to the benefits gained from reducing the impacts of climate change on health. Co-benefits are delivered through key pathways, such as reductions in air pollution from replacing fossil fuels with clean, renewable energy sources; consumption of healthy, sustainable diets; and the promotion of active travel and use of public transport. To capitalise on these additional health gains, while reducing inequities and meeting climate targets, health co-benefits must be incorporated into the delivery of the Paris Climate Agreement including through nationally determined contributions and long-term low greenhouse gas emission development strategies. Improved monitoring of progress alongside better harmonised research can support ambitious climate action. A greater emphasis must be placed on estimating the magnitude of both the health and greenhouse gas effects of implemented mitigation actions, including through processes such as the Global Stocktake. Future research should use consistent methods and descriptions of objectives, settings, and assumptions to support informed decision making and inclusion in national and global policy. Integrated evaluation of actions can also ensure implementation achieves equitable delivery of benefits and minimises trade-offs. Systems approaches are needed; achievement of transformative change across sectors to achieve improved health equity at net-zero greenhouse gas emissions requires systems approaches that integrate adaptation and mitigation and address underlying structures driving inequity and rising greenhouse gas emissions. Examples of implemented and evaluated transformative action are urgently needed to inspire and inform change. A coalition of organisations, and subnational and national initiatives, is proposed to accelerate progress towards net-zero greenhouse gas emissions and improve health, with a commitment to monitor and evaluate effects on health and greenhouse gas emissions as well as to share experiences about successes and failures.