Transdisciplinary research (TDR) integrates academic and non-academic expertise to co-produce actionable knowledge that contributes to societal impact in addressing sustainability challenges. While context is widely acknowledged as important, the role and definition of context factors shaping TDR remain underexplored. This study develops an integrative understanding of context by synthesising theoretical literature and analysing 17 semi-structured interviews from international TDR case studies. We identify nine key context factors across three categories: outer factors (outside projects), inner factors (within projects), and temporal/ spatial dimensions (project boundaries). These context factors influence collaborative research processes in different ways across projects, requiring ongoing reflexivity and adaptation. Positionality awareness and ethics are central in shaping power dynamics, stakeholder engagement, and knowledge-co-production, highlighting the need for context-sensitive approaches. To support this in a structured way, we present a framework linking context with research design, process, methods and outcomes. Additionally, we provide a set of reflective questions for researchers and practitioners to identify, assess, and respond to contextual influences that shape stainability transformations. By advancing a more systematic understanding of context, this study contributes to building reflexive and inclusive approaches to transdisciplinary collaboration.