Attention-deficit/hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD) are both externalising behaviour disorders that are associated with negative outcomes for the individuals displaying symptoms. Therefore, establishing early predictors and protective factors of these disorders is important for preventative intervention development. Emotion regulation is a recognised component of both disorders and mindful parenting is emerging as a potential protective factor in psychopathological development. The current study aims to examine if emotion regulation at age 6 can predict ADHD and/or ODD symptoms at age 9. Furthermore, it aims to investigate if mindful parenting moderates these potential relationships. The current longitudinal study used a non-clinical sample, consisting of 64 children and their caregivers. Emotion regulation and mindful parenting levels were measured when the children were age 6, and symptoms of ADHD and ODD were measured at age 9. Simple regression analyses and moderation analyses were conducted in order to investigate the research questions. Results showed that emotion regulation at age 6 predicted both ADHD and ODD symptoms at age 9. However, mindful parenting seemed to only have a somewhat moderating effect on the relationship between emotion regulation and ADHD symptoms, not ODD symptoms. These results indicate that emotion regulation abilities at a young age are important to focus on when designing preventative interventions for externalising behaviour disorders. Mindful parenting could also be considered to be included in interventions for ADHD, however further research is needed.