A strong primary healthcare system that is effective and efficient is a priority for health reform in Australia. Commissioning to support primary healthcare delivery has received increasing attention as part of healthcare reform in Australia and beyond. The aim of this paper is to present a case study of transitioning to an activity-based model for the provision of GP after-hours services in Australia. The GP After-Hours Program utilised a commissioning model that comprised of needs assessment, service development, provider engagement and evaluation. Evaluation of the new model showed a 17% increase in after-hours services, with service providers indicating that they were satisfied with the new process. Examination of the experience of implementation suggests that the commissioning model provided a useful framework for guiding activity-based funding for after-hours services. However, relational factors, such as engagement with the community, knowledge of the wider context and legitimacy of the commissioning body, can affect the implementation process.