Introduction: New guidance, from NHS England (Saving Babies Lives Care Bundle Version 2 Element 5 (SBLCBv2)) has recommended a best practice pathway for women at risk of preterm birth (the Preterm Birth Pathway). This is to help meet the Department of Health’s aim to reduce preterm birth from 8% to 6% by 2025. Considering most hospitals do not currently have a preterm prevention clinic, implementing this pathway will require significant coordination. Methods and analysis: The study will aim to investigate key features of contexts, mechanisms and outcomes, and their interactions in the implementation of the asymptomatic prediction and prevention components of the SBLCBv2 Preterm Birth Surveillance Pathway. This will be through a theory driven realist evaluation, utilising mixed methods (interviews with staff and women, observational analysis and analysing routinely collected hospital and admin data) in three case sites in England. The study has a Project Advisory Group composed of five women who have recently given birth. Ethics and dissemination: The study has ethical approval (King’s College London REC approval number: MRSP-20/21-20955, and, IRAS:289144). A dissemination plan will be fully created with the Project Advisory Group, and we anticipate this will include presenting at conferences, publications, webinars, alongside dissemination to the wider population through parent and baby groups, the media and charities. Trial registration number: ISRCTN57127874.