Social opposition is the face-to-face unwillingness or incapacity to compromise. Deficits in social cooperation can undermine both individual and societal wellbeing, adversely affecting both low and high-income countries (Global Peace Index, 2021).Empirical and theoretical research from developmental psychology and developmental psychobiology suggest that compulsive social oppositionalism may be influenced by physiological regulation capacities which are shaped by early life experiences.  The goal of this study was to investigate a possible long-term effect of early life experience on child oppositionalism, specifically physiological regulation as measured by cardiac vagal functioning. Observed quality of maternal parenting was assessed at 12 months of age (N=138 mother-child dyads) through the Keys to Interactive Parenting Scale (KIPS; Comfort & Gordon, 2006) and child cardiac vagal regulation (RSA; respiratory sinus arrhythmia) and social oppositionalism were assessed five years later. Structural equation modeling that included a latent basis coefficient model of cardiac vagal regulation was examined, providing the investigation of both tonic and flexible cardiac vagal regulation.Quality of maternal parenting consistently related to child flexible cardiac vagal regulation across both relaxing and stress conditions. Higher scores on quality of parenting at 12 months of age related to increased cardiac vagal flexibility years later, allowing children greater physiological adaptability. Child flexible cardiac vagal regulation as assessed by recovery from stress also related to decreased child social oppositionalism. In addition, higher child tonic cardiac vagal tone was related to lower child social oppositionalism suggesting that, regardless of condition, greater physiological regulation influenced lower child social oppositionalism. Lastly, the direct effect of parenting quality in early life on child social oppositionalism years later was not evident, providing evidence for the importance of child physiological regulation.Efforts to increase quality of maternal parenting for children in early life may carry long-term effects on both child physiological development and social outcomes. In addition, because cardiac vagal regulation is a major neurobiological building block of wellbeing and resilience, supporting caregivers in their efforts to care for children in the first year of life may impact physical and social capacities across the lifespan. This may help build individuals who not only have physiological regulatory capacities needed for health and resilience but social engagement skills that facilitate wellbeing for all members of society.