Midwifery continuity of carer (MCC) models result in better clinical outcomes for women and offer midwives a superior way of working when compared to other models of maternity care. Implementing a MCC model, a key recommendation of the Scottish Government Maternity and Neonatal Strategy Best Start, requires significant restructuring of maternity services and changes to midwives’ roles. Careful evaluation is therefore required to monitor and understand how the policy affects care providers and users. Realist evaluation is an appropriate methodology for evaluating programmes of change set within complex social organisations, such as health services, and can help to understand variations in outcomes and experiences. This paper presents the approach taken using the principles of realist evaluation to identify key programme theories, which then informed an evaluation framework and a midwives’ evaluation tool. The comprehensive survey-tool developed for midwives has the potential to be used more widely to evaluate comparable strategic change in this area.