In the decade since the first observationally based empirical studies of coparenting process in nuclear families made their mark, most investigations of early coparenting dynamics have examined whether and how such dynamics drive child development trajectories, rather than identifying factors that may contribute to the differential development of such dynamics in the first place. In this prospective study, we examined both individual-representational and dyadic-interpersonal predictors of early coparental process. Fifty married couples expecting their first child portrayed their expectations and concerns about family life after the baby’s arrival, and took part in a set of problem-solving tasks used to help evaluate marital quality. Both mothers’ and fathers’ prebaby expectations about the future family, and prenatal marital quality, predicted observed coparenting cohesion at 3 months postpartum. Maternal– and marriage–coparenting trajectories differed as a function of infant characteristics, with pathways most pronounced when infants were rated high in negative reactivity. Results reveal how the prenatal environment can come to shape early coparenting process, and indicate that family models must take into account the role that child characteristics can play in altering prebirth–postpartum pathways.