Many autistic adolescents and young adults present with aggressive behaviours, which can be challenging for caregivers. The present study aimed to explore the underlying mechanisms between social communication understanding and aggressive behaviours in autistic and non-autistic adolescents, specifically the role of emotional dysregulation and its impact on avoidance with caregivers. Caregivers of autistic (n = 275) and non-autistic adolescents (n = 123) completed standardised caregiver-report questionnaires measuring social communication understanding, emotional dysregulation, avoidance between the adolescent and caregiver and aggressive behaviours. A serial mediation analysis indicated that levels of social communication understanding were indirectly associated with aggressive behaviours. This occurred through increased emotional dysregulation, which may have led to increased avoidance between the autistic and non-autistic adolescents and their caregivers. These findings support a sequential process by which adolescents with low social communication understanding are more likely to behave aggressively through being emotionally dysregulated and the impact of this on the increased avoidance within the caregiver--adolescent dyad. This process was found within autistic and non-autistic adolescents, suggesting a mechanism across individuals with aggression. These findings indicate that interventions based on improving emotion regulation ability and responses between adolescents and their caregivers may aid in reducing aggressive behaviours in adolescents and young adults with lower social communication understanding.