"Participation of relevant stakeholders, knowledge integration, responsive and emergent design and effective boundary management are four key features of transdisciplinary research (TDR). These features pose significant challenges to both undertaking TDR and evaluating its societal impact. We argue that TDR’s context specificity and complexity warrant an evaluation approach that supports the coordinating team in developing these key features. In light of this, this article aims to reconcile two distinct foci of TDR evaluation, namely supporting transdisciplinary capacity building and impact evaluation. We share the results from a combined approach in which the authors acted both as facilitators and evaluators of a TDR project, to conduct an embedded, formative evaluation. Our findings show that the approach allowed for better access to the participants and sensitivity to their perspectives on impact, and for enhanced understanding of complex internal and external project dynamics and how these shaped the project. This resulted in a meaningful assessment of TDR’s societal impacts and enabled attributing these to specific process elements. Moreover, the approach supported the coordinating TDR team’s capacities for developing key TDR features. Four TDR capacities were identified: building TDR ownership, openness and transparency for integrating divergent TDR needs, purposeful responsiveness to emergent TDR needs and navigating institutional realities and TDR ambitions. The approach presented may serve as stepping stone for the TDR community to further the conversation on (the impact of) inclusive, reflexive and responsive research."