Previous research assessing public organisations in the delivery of infrastructure projects mainly focuses on public project delivery organisations and their interaction with private parties. However, many challenges experienced by these project delivery organisations relate to the interaction with the public parent organisation. In practice, this interface mainly materialises as the interaction between the internal commissioner (Dutch: ambtelijk intern opdrachtgever) and the project manager. Internal commissioners are appointed to control whether project organisations adhere to the project assignment. Due to dynamic complexity emerging in infrastructure projects, causing deviations from the defined project assignment, more commitment of these commissioners to projects is needed by these public managers during project realisation. By qualitative research in diverse Dutch public sector organisations, more insight into the internal commissioning role during project realisation is created. The research suggests several ways of improving the efficiency of internal working procedures in public parent organisations. Furthermore, the research identified management recommendations for improving professionalism in the internal commissioning role during project realisation.