Aims To explore which conditions of community engagement are implicated in effective interventions targeting disadvantaged pregnant women and new mothers. Background Adaptive experiences during pregnancy and the early years are key to reducing health inequalities in women and children worldwide. Public health nurses, health visitors and community midwives are well placed to address such disadvantage, often using community engagement strategies. Such interventions are complex; however, and we need to better understand which aspects of community engagement are aligned with effectiveness. Design Qualitative comparative analysis conducted in 2013, of trials data included in a recently published systematic review. Methods Two reviewers agreed on relevant conditions from 24 maternity or early years intervention studies examining four models of community engagement. Effect size estimates were converted into ‘fuzzy’ effectiveness categories and truth tables were constructed. Using fsQCA software, Boolean minimization identified solution sets. Random effects multiple regression and fsQCA were conducted to rule out risk of methodological bias. Results/findings Studies focused on antenatal, immunization, breastfeeding and early professional intervention outcomes. Peer delivery (consistency 0·83; unique coverage 0·63); and mother‐professional collaboration (consistency 0·833; unique coverage 0·21) were moderately aligned with effective interventions. Community‐identified health need plus consultation/collaboration in intervention design and leading on delivery were weakly aligned with ‘not effective’ interventions (consistency 0·78; unique coverage 0·29). Conclusions For disadvantaged new and expectant mothers, peer or collaborative delivery models could be used in interventions. A need exists to design and test community engagement interventions in other areas of maternity and early years care and to further evaluate models of empowerment.