This longitudinal study aimed to validate the biosocial theory of borderline personality disorder (BPD) by examining the transactional relationship between individual vulnerabilities and parental invalidation, and their links to BPD symptoms. We recruited a sample of 332 adolescents (mean age = 14.18 years; 58.3% female) residing in Singapore and administered self-report measures across three time-points (six months apart). Results from our path analytic model indicated that parental invalidation, impulsivity, and emotional vulnerability exhibited unique predictive associations with emotion dysregulation six months later. There was also a reciprocal prospective relationship between emotion regulation difficulties and BPD symptoms. Using random-intercepts cross-lagged panel models, we found partial evidence for a within-individual reciprocal relationship between parental invalidation and emotional vulnerability, and a unidirectional relationship of within-individual changes in impulsivity positively predicting changes in parental invalidation six months later. Overall, the study provided partial empirical support for the biosocial model in a Singaporean context.