The development of insecure attachment relationships in the offspring of mothers with major depressive disorder (MDD) may initiate a negative trajectory leading to future psychopathology. Therefore, the provision of theoretically guided interventions designed to promote secure attachment is of paramount importance. Mothers who had experienced MDD since their child’s birth were recruited (n = 130) and randomized to toddler-parent psychotherapy (DI) or to a control group (DC). Nondepressed mothers with no current or history of major mental disorder and their toddlers also were recruited for a nondepressed comparison group (NC; n = 68). Children averaged 20.34 months of age at the initial assessment. Higher rates of insecure attachment were present in both the DI and the DC groups at baseline, relative to the NC group. At postintervention, at age 36 months, insecure attachment continued to predominate in the DC group. In contrast, the rate of secure attachment had increased substantially in the DI group and was higher than that for the DC and the NC groups. These results demonstrate the efficacy of toddler-parent psychotherapy in fostering secure attachment relationships in young children of depressed mothers.