Conceptually grounded, integrated, city-scale and comparative studies remain rare and are based mostly on meta-reviews of the literature or broad surveys. Conversely, debates about the limitations of incremental or transitional change and exhortations towards more ambitious processes of system or transformative changes are rarely grounded in adequate empirical analysis. Accordingly, this paper examines city-scale plans and actions in order to throw light on these issues in a carefully contextualised Global South–North comparison between Cape Town, South Africa, and Greater Manchester, UK. Cape Town has a considerable pedigree of citywide climate policy and action but achieving cross-departmental integration remains a key challenge, along with operationalisation and monitoring. Greater Manchester has abundant climate ambitions to become a leading European green city, but recent innovative policy processes revealed a lack of capacity and in-house expertise. The comparative analysis therefore focuses on capacity constraints hampering fulfilment of progressive city aspirations that engage with global agendas, and on how they use innovative planning and implementation processes and different forms of knowledge to address integrative or cross-cutting issues, as well as on their relative success to date in doing so in the face of different extents of inequality and power asymmetry. <em><strong>Policy relevance</strong></em> A comparative analysis of city-wide climate policy initiatives provides four insights that are highly relevant for policymakers. First, the political–institutional context in which local climate policy is designed invariably shapes the policy process, making it imperative to consider redesigning the ‘multilevel governance’ structures between the local governments that ‘hold the problem’ of climate change with the tools required to address the root causes. Second, policymakers need to grapple with and negotiate across the conflicting rationalities held by different professionals and stakeholders to bring together and integrate different types of knowledge into a comprehensive perspective. Third, local governments must find ways to address the underlying challenge of institutional inertia to embrace more ambitious, transformative policy agendas, moving away from incrementalist approaches. Finally, local governments should integrate debates on socio-spatial fairness and justice with climate policy, recognising the interdependencies between these agendas.