Early-life adversity increases the risk of health problems. Interventions supporting protective and responsive caregiving offer a promising approach to attenuating adversity-induced changes in stress-sensitive biomarkers. This study tested whether participation in an evidence-based dyadic psychosocial intervention, child–parent psychotherapy (CPP), was related to lower epigenetic age acceleration, a trauma-sensitive biomarker of accelerated biological aging that is associated with later health impairment, in a sample of children with trauma histories. Within this quasi-experimental, repeated-measures study, we examined epigenetic age acceleration at baseline and postintervention in a low-income sample of children receiving CPP treatment ( n = 45; age range = 2–6 years; 76% Latino) compared with a weighted, propensity-matched community-comparison sample ( n = 110; age range = 3–6 years; 40% Latino). Baseline epigenetic age acceleration was equivalent across groups. However, posttreatment, epigenetic age acceleration in the treatment group was lower than in the matched community sample. Findings highlight the potential for a dyadic psychosocial intervention to ameliorate accelerated biological aging in trauma-exposed children.