Abstract Background Tommy’s Pathway: Clinical Decision Support Tool (the Tool/the Tommy’s Pathway), a web-based application for assessing risk of preterm birth and placental dysfunction, is provided as a dual-interface web-application, used by maternity care providers and maternity service users. The Tool utilises validated algorithms and rule engines to offer a more sophisticated assessment of risk than traditional checklist methods and offers instantaneous decision support by providing care recommendations according to risk and in line with evidenced-based clinical guidance. This novel intervention has the potential to reduce variation in care that could contribute to the higher rates of preterm birth and stillbirth seen in those from ethnic minority and socially deprived groups. We evaluated implementation of the Tommy’s Tool in five early-adopter NHS hospitals to inform a cluster randomised controlled trial. Methods We used online surveys, semi-structured interviews and focus groups to investigate: maternity service user and healthcare professional (HCP) experience; barriers and facilitators to implementation; reach (whether particular groups are excluded and why), fidelity (degree to which the intervention is delivered as intended), and unintended consequences. The NASSS framework (Non-adoption or Abandonment of technology by individuals and difficulties achieving Scale-up, Spread and Sustainability) informed analysis. Results 1181 women and 112 HCPs participated, completing 1260 online surveys, 8 focus groups and 29 semi-structured interviews. Findings highlighted the importance of ensuring the Tool was used in routine care management for all eligible service users. This informed development of an additional functionality to ensure that HCPs were able to create profiles for those who were unable or unwilling to sign up and create a profile themselves. Before this feature was introduced the proportion of service users registered on the Tool, was ~ 70%, compared to ~ 90% afterwards. Proportions of women from Asian and black ethnic groups, and those from the most deprived areas (IMD quintiles 1 & 2), also increased after the change, from 14.6%, 5.8% and 40.9% (of all maternity service users), to 16.9%, 14.2% and 52.4%, respectively. Further refinements will include translation into non-English languages. Conclusions The Tommy’s Tool has the potential to make the provision of optimal maternity care easier for healthcare professionals, which could reduce variation in care and ultimately improve outcomes. This study gave us the opportunity to evaluate early adopter implementation in order to optimise the Tool and its implementation strategy ahead of a cluster randomised controlled trial. Trial registration This study was prospectively registered on ISRCTN: ID13498237, on 31/01/2022.