Infants’ high negative affectivity often initiates maladaptive parent-child relational processes that may involve both the parent’s and the child’s sides of the relationship. We proposed that infants’ high negative affectivity triggers distinct sequelae in dyads classified as avoidant, resistant, and disorganized, compared to secure dyads. In 200 community families, at 8 months, we observed infants’ negative affectivity; at 16 months, we assessed attachment organization and collected observations and reports of parent-related (responsiveness, resentment of child, power assertion, and intrusiveness) and child-related (social-emotional competence, opposition, and anger) constructs. In mother-child avoidant dyads, infants’ high negative affectivity was a significant precursor of mothers’ higher resentment and intrusiveness and children’s lower social-emotional competence. Those associations were significantly different than in secure dyads (in which none were significant). In father-child disorganized dyads, infants’ high negative affectivity was a significant precursor of fathers’ lower responsiveness and higher resentment; there were no association in secure dyads. Regardless of infants’ negative affectivity, compared to secure dyads, parents in resistant dyads expressed more resentment of child, and avoidant and resistant children were more oppositional to their fathers. The study illustrates multifinality in parent- and child-related processes that characterize unfolding early relational dynamics in dyads differing in just-emerging attachment.