Both maternal and paternal supportive parenting (i.e., sensitivity, warmth, stimulation, and engagement) across early childhood have been found to be associated with multiple domains of children's positive socioemotional functioning. However, few studies have considered how maternal and paternal supportive parenting may interact to impact child development. Thus, the present study assessed direct and moderated longitudinal relations between maternal and paternal supportive parenting in toddlerhood (24 and 36 months, respectively) and fathers' and teachers' reports of children's socioemotional and behavioral adjustment in first grade. Data were drawn from a large, sample of Norwegian parents and children (N = 455, 51% female, 49% male, 10% endorsed financial strain, 75% of fathers and 86% of mothers born in Norway). After controlling for child temperamental activity level and soothability in infancy, path analysis revealed that higher paternal supportive parenting was associated with fewer symptoms of father-reported child hyperactivity/impulsivity in first grade. In addition, a significant interaction between maternal and paternal supportive parenting was evident for three out of the four assessed outcomes (per both father- and teacher-reports): externalizing problems, hyperactivity/impulsivity symptoms, and social skills. Simple slope analyses revealed a negative relation between parental supportive parenting and children's externalizing (father-reported) and hyperactivity/impulsivity problems (father- and teacher-reported) when the child's other parent engaged in low levels of supportive parenting. Similarly, paternal supportive parenting was positively associated with children's social skills (father-report) when mothers engaged in low levels of supportive parenting. Results are discussed with implications for including both mothers and fathers in early childhood research, intervention, and social policy.