Intermediation and transformative capacity building are identified as important issues in sustainability transformations. Yet the connection of these two concepts has not been systematically analysed. This empirical, qualitative case study on active transport in Finland investigates intermediation in building local transformative capacity. The study shows that intermediaries are a heterogeneous group of actors that support transformative capacity building by facilitating the flows of knowledge, linking actors, forming ties across different scales, and supporting visioning and strategic planning. Intermediation manifests in five of the seven elements of local transformative capacity building. Our study, thus, contrasts with previous understanding wherein intermediation is considered only as a criterion for multiform governance. As intermediation is central in building transformative capacity, it should be better acknowledged, particularly by authorities and policymakers to secure legitimacy, operational capabilities, and funding for intermediaries.