Project and strategic management scholarship recognises the importance of project capabilities that allow firms to deliver projects. Although work on project capabilities is a fast-growing line of inquiry, little is still known about how clients assemble project capabilities to achieve operational outcomes in inter-organisational settings. This study seeks to apply theoretical work on project capabilities to the domain of infrastructure project delivery in order to understand how the assembly of project capabilities in temporary inter-organisational settings contributes to the delivery of operational outcomes. The empirical enquiry takes place in the context of the delivery of London Heathrow Terminal 2. Through an inductive theory building approach drawing upon semi-structured interviews with client-side project leadership, internal documents, publicly available data and ongoing engagement with the field, we identified three key capability-enabling mechanisms that help explain the genesis of project capabilities in inter-organisational settings: (1) reconfiguring project capabilities, (2) adapting project capabilities and (3) maintaining project capabilities. We discuss and expand these findings by engaging with theoretical ideas from project studies, and mainstream strategy, organisation, and management research to induce a dynamic model that can be helpful to guide future research, policy and management practices relating to the client side management of project capabilities. •Paper focuses on project capabilities (PCs) for operational outcomes in inter-organisational settings.•Paper presents an inductive qualitative study of the delivery of London Heathrow Terminal 2.•Findings suggest three key capability-enabling mechanisms in the case project.•Findings are used to develop a dynamic PC model for operational outcomes in inter-organisational settings.•Paper concludes with theoretical contributions for project and strategic management scholarship.