Background: Concern about the poor care of some people with an intellectual disability has highlighted the need for systemic, large-scale interventions to develop a skilled workforce. Method: We outline how an implementation science theoretical model informed the development of a region-wide Positive Behavioural Support (PBS) Workforce Development (WFD) approach. Results: We provide an example of the application of the model in practice and demonstrate how this enabled us to understand the competencies and development needs of the workforce; engage effectively with stakeholders; and develop, deliver and evaluate a PBS WFD model. Conclusion: The application of the model helped us to identify, prioritise, and address the multiple and complex factors that were relevant to the implementation of the PBS WFD approach.