Background Echoing international trends, the most recent United Kingdom reports of infant and maternal mortality found that pregnancies to women with social risk factors are over 50% more likely to end in stillbirth or neonatal death and carry an increased risk of premature birth and maternal death. The aim of this realist synthesis was to uncover the mechanisms that affect women's experiences of maternity care. Methods Using realist methodology, 22 papers exploring how women with a wide range of social risk factors experience maternity care in the United Kingdom were included. The data extraction process identified contexts (C), mechanisms (M), and outcomes (0). Results Three themes, Resources, Relationships, and Candidacy, overarched eight CMO configurations. Access to services, appropriate education, interpreters, practical support, and continuity of care were particularly relevant for women who are unfamiliar with the United Kingdom system and those living chaotic lives. For women with experience of trauma, or those who lack a sense of control, a trusting relationship with a health care professional was key to regaining trust. Many women who have social care involvement during their pregnancy perceive health care services as a system of surveillance rather than support, impacting on their engagement. This, as well as experiences of paternalistic care and discrimination, could be mitigated through the ability to develop trusting relationships. Conclusions The findings provide underlying theory and practical guidance on how to develop safe services that aim to reduce inequalities in women's experiences and birth outcomes.