Attachment security can act as an inner resource to promote women’s adjustment to motherhood. However, the mechanisms explaining the relationship between attachment representations and maternal adaptation outcomes are not well understood. This study aimed to examine the direct and indirect effects of attachment representations on maternal confidence, through postpartum negative automatic thoughts and depressive symptoms. The sample consisted of 387 postpartum women who completed a cross-sectional online survey including measures of attachment representations, depressive symptoms, postpartum negative automatic thoughts and maternal confidence. Our results showed a significant relationship between more insecure attachment representations and higher depressive symptoms (p < .001), but also with more frequent postpartum negative automatic thoughts (p < .001); depressive symptoms and postpartum negative automatic thoughts were also inversely associated with women’s maternal confidence (p < .001). Moreover, indirect effects of attachment representations on maternal confidence were found, but only through postpartum negative thoughts [attachment-related anxiety: 95% CI = −0.03/−0.01; attachment-related avoidance: 95% CI = −0.05/−0.01]. The results of the present study emphasize the important role of the cognitive component of depressive symptomatology (postpartum negative automatic thoughts) in the relationship between attachment representations and maternal confidence, allowing to draw specific implications. We highlight the implications for clinical practice during the perinatal period to address both negative thoughts and women’s maternal confidence.