Background: New parents' postpartum sexual satisfaction and function is often disrupted. Poor postpartum mental health, such as symptoms of childbirth-related posttraumatic stress disorder (CB-PTSD), may increase the risk of experiencing sexual difficulties. Aim: To investigate the prospective association between mothers'/birthing parents' and fathers'/non-birthing parents' CB-PTSD symptoms at 8 weeks postpartum and their own and their partners' overall sexual satisfaction and postpartum-specific sexual function at 6 months postpartum. Methods: We used data from 344 couples, who were mostly recruited at maternity hospitals in Dresden, Germany. Parents' birth characteristics and CB-PTSD symptoms (City Birth Trauma Scale) were assessed during a structured telephone interview at 8 weeks postpartum and their depression symptoms (Edinburgh Postnatal Depression Scale) were assessed via online survey at 6 months postpartum. Data were analyzed using Actor-Partner Interdependence Models and multiple regression analyses. Outcomes: An online questionnaire at 6 months postpartum assessed overall sexual satisfaction with a single item and postpartum sexual function using the Sexual Function Questionnaire's Medical Impact Scale, previously adapted and validated for the impact of childbirth. Results: Both parents' higher CB-PTSD symptoms at 8 weeks postpartum predicted their own lower sexual satisfaction at 6 months postpartum. When adding perineal lacerations and parents' depressive symptoms at 6 months postpartum, these effects were no longer significant. Instead, fathers'/non-birthing parents' higher depressive symptoms at 6 months postpartum was associated with their own lower sexual satisfaction at 6 months postpartum. Mothers'/birthing parents' higher CB-PTSD symptoms at 8 weeks postpartum predicted their own higher postpartum sexual function problems at 6 months postpartum, even when controlling for postpartum depression. Fathers'/non-birthing parents' depression symptoms also predicted mothers'/birthing parents' postpartum sexual function. Clinical implications: Findings highlight the importance of postpartum mental health screenings for both parents, integration of sexual health discussions into routine care, and couple-focused interventions to support parents' postpartum sexual satisfaction and function. Strengths and limitations: This study is the first to prospectively and dyadically examine the associations between CB-PTSD symptoms and overall sexual satisfaction and postpartum-specific sexual function. Limitations include a lack of sample diversity, low endorsement of CB-PTSD symptoms, use of a one-item sexual satisfaction measure, and poor reliability of the sexual function measure for fathers/non-birthing parents. Conclusions: Our findings suggest that new parents' CB-PTSD symptoms in the early postpartum are not associated with their sexual satisfaction over and above postpartum depression symptoms. However, for mothers/birthing parents, greater CB-PTSD symptoms were associated with poorer postpartum sexual function at 6 months.