While associations between exposure to marital conflict and child development have been documented extensively in middle childhood and adolescence, few studies have examined the developmental consequences of conflict exposure in infancy. Moreover, those that have examined marital conflict in infancy tended to focus on consequences of conflict exposure on infants' attachment security, and various aspects of infants' physiological and emotion regulation. Virtually nothing is known about the longitudinal links between exposure to interparental conflict in infancy and later cognitive development. Using longitudinal data on a subsample of infants (N = 6,019) and their parents who participated in the Early Childhood Longitudinal Study, Birth Cohort (ECLS-B), this study examined links between the frequency of interparental conflict at 9 months and child cognitive development 15 months later. Combining data from parent interviews, birth certificates, in-home assessments of child cognitive development, and videotaped parent-child interactions, results showed significant negative associations between the frequency of child-related interparental conflict at 9 months of age and child cognitive ability at 24 months. The negative association reflects a direct effect that was not mediated by parental support or child attachment security measured at 24 months. Associations were calculated while considering children's prior cognitive functioning (at 9 months), and a wide range of child, parent and household characteristics.