Ecosystem-based adaptation (i.e. the use of ecosystem services to adapt to climate change) and its mainstreaming into municipal planning to foster sustainable transformation is receiving increasing interest from both academic and governmental bodies. However, little is known about the pathways for its systematic implementation, or the extent to which it is already mainstreamed in municipal planning practice. This article reports on a study in which local pathways to sustainably mainstream ecosystem-based adaptation were compared in 12 municipalities in Germany and Sweden. The results show that while progress is seemingly similar in the two countries, there are noticeable differences regarding the local triggers, the importance given to particular mainstreaming strategies and their link to climate policy integration. Ecosystem-based approaches to climate change adaptation are not labelled or systematised in either country. In addition, the mainstreaming of ecosystem-based adaptation is enabled through municipalities’ level of experience in mainstreaming other issues. In Sweden, the ecosystem service concept drives adaptation mainstreaming, which is often disconnected from the integration of climate mitigation policy. In contrast, German structures and planning processes established for climate change mitigation are paving the way. We conclude that systematic adaptation mainstreaming and its potential linkages and disconnects with climate mitigation policy integration require more explicit consideration, both in research and practice. We call for more research on the role of inclusive (as opposed to fragmented) climate policy integration to assure sustainable planning and transformation.