While greenhouse gas emissions in Europe have reduced in recent years, there is still a considerable gap between the current situation and where we need be to limit global warming and adapt to climate change, particularly in cities. The Sustainable Development Goals and the Climate Agenda have placed great emphasis on collaborative frameworks and the private sector’s crucial contribution to closing the climate gap in terms of investment and leadership in innovation. However, there has not been a concise follow-up and assessment of the private sector’s practical involvement and contribution, whether policy and legislative frameworks and planning approaches are suitable to enable this involvement, and who would lead in delivering the climate agenda locally. The present article addresses this gap reporting on case observations regarding the delivery of climate interest and sustainability through urban development in London and Copenhagen—two European cities of different sizes and varying government approaches. Thereby, the article assesses patterns of private-sector involvement and governance around climate adaptation and mitigation and locates gaps around its involvement in delivering the climate agenda. The analysis clarifies overarching differences in governance and frameworks for the involvement of the private sector between the two cities, attributing this on the local level partly to city size and scale, but to a great extent to ‘city leadership’ in the built environment and sustainable urban innovation in general. A crucial finding highlights the importance that cities further establish platforms for collaborative learning, specifically around pilot urban projects, thereby stimulating voluntary private engagement. Another key finding is in the potential effectiveness of strategies by public agencies such as city governments to incentivise private actors and simultaneously monitor sustainability effects both broadly at the city level, and specifically at urban project level using ecological, circular and life-cycle approaches. Further implications of the analysis point to the importance of developing a more nuanced approach to understanding the different roles fulfilled by the ‘private sector’ in the built environment and the necessity of creating an information base addressing the life cycle of development projects and business processes and comparing their impacts. The situation also necessitates considering efforts, impacts, climate finances and data on the broad city scale. The findings of this article can inspire further research, benefit further action in these cities and inform international efforts about climate gaps related to climate adaptation and mitigation.