Maternal self-efficacy predicts sensitive and responsive caregiving. Low maternal self-efficacy is associated with a higher incidence of postpartum depression. Maternal self-efficacy and postpartum depression can both be buffered by social support. Maternal self-efficacy and postpartum depression have both been linked independently, albeit in separate studies, to the experience of violent trauma, childhood maltreatment, and spousal abuse. This study proposed a model in which postpartum depression mediates the relation between attachment trauma and maternal self-efficacy, with emotional support as a moderator. Participants were 278 first-time mothers of infants under 14 months. Cross-sectional data were collected online. Mothers completed questionnaires on attachment trauma, maternal self-efficacy, postpartum depression, and emotional support. A moderated mediation model was tested in a structural equation modeling framework using Mplus’ estimate of indirect effects. Postpartum depression fully mediated the relation between trauma and maternal self-efficacy. Emotional support moderated only the pathway between postpartum depression and maternal self-efficacy. Attachment trauma's implications for maternal self-efficacy should be understood in the context of overall mental health. Mothers at the greatest risk for low maternal self-efficacy related to attachment trauma also are those suffering from postpartum depression. Emotional support buffered mothers from postpartum depression, though, which has implications for intervention and future research.