Creating scientifically rigorous and user-friendly data visualisations can play a critical role in making complex information more accessible to wider audiences and supporting informed decision-making. ‘Co-design’ encapsulates a way of approaching data visualisation that ensures a deep and shared understanding between those creating the visuals (e.g. information designers, content experts, cognitive scientists) and the audience/users. This essay describes co-designing data visualisations with the Intergovernmental Panel on Climate Change (IPCC). A multidisciplinary design team made up of information designers and cognitive and social scientists worked closely with IPCC authors and staff to develop data visualisations for the Summary for Policymakers (SPM) of the Special Report on Global Warming of 1.5 °C and the Special Report on Climate Change and Land. In this essay, the authors consider the three crucial elements that underpin a successful co-design process—practical tools and a flexible method; cognitive science and psychology to better understand the needs of users; and the importance of trust and leadership. The authors reflect on the application of the co-design approach in an IPCC context, noting specific challenges and including recommendations for future IPCC reports. The mutual learning experience of the special reports indicates a shift towards a design culture within parts of the IPCC that recognises the value of telling a compelling visual story while retaining scientific integrity—an approach that has been retained for the Working Group I contribution to the Sixth Assessment Report.