The planetary health concept describes the relations between health and climate. The inequities that connect these two domains are experienced most by low-resource and vulnerable populations, e.g. the impact of drought on subsistence livelihoods and associated mental health issues. Climate justice and health justice are framed through capabilities and integrated with ecofeminist approaches. Spatial justice is introduced as the ability to conceptualise how these interconnected injustices are mediated through environments. The integration of these theories can provide a justice-based planetary health approach that could overcome several barriers. Design and spatial practice offer processes and tools to understand the complexity of planetary health across scales, systems and relations; and to generate design solutions that promote equity and justice. Practical examples of Global South design projects are presented that connect health and climate. The example of a maternal health project in rural Kenya shows how a conceptual design framework for a justice-based planetary health can contribute to the planetary health.