Skin conductance level reactivity (SCLR) was examined as a longitudinal mediator and moderator of relations between parental marital conflict and psychopathology among children and young adolescents. Participants were 157 boys and girls (M age at T1 = 9.31 years; SD = 1.97); there was a 2-year lag between T1 and T2 assessments. At T1, participants’ SCLR was assessed in response to lab challenges. Parents completed measures of aggressive marital conflict and child adjustment at T1 and T2. Supportive of moderation effects, T1 marital conflict interacted with T1 SCLR and gender in the prediction of changes in maladjustment. The link between marital conflict and increased internalizing and externalizing symptoms was stronger for girls with higher SCLR than girls with lower SCLR. Marital conflict predicted increased externalizing behaviors for boys with lower SCLR but not higher SCLR, although levels of externalizing behaviors were similar among boys with lower and higher SCLR especially at higher levels of marital conflict. Findings build on the literature by illustrating the importance of examinations of both family risk and youth biological vulnerability for the prediction of psychopathology.