There is limited literature on the association between parenting practices, parenting stress and externalising behaviours in autistic children. We investigated whether parenting practices mediate the association between parenting stress and externalising behaviours. Parents of school-aged autistic children (n = 138) completed an online survey on parenting practices, parenting stress and child externalising behaviours. Higher levels of parenting stress were associated with higher levels of externalising behaviours. In contrast to prior literature, parenting practices were not associated with child externalising behaviours and did not have mediating effects on the association between parenting stress and child externalising behaviours. However, higher levels of parenting stress were associated with lower levels of mindful parenting and higher levels of permissive and authoritarian parenting practices. Together, findings suggest that targeting parenting stress can impact parenting practices. Limitations of the study are acknowledged including the cross-sectional design, which limits causality-based inferences, given parent–child associations could occur over time. Implications for research and clinical practice in designing parent-informed programmes focused on reducing parenting stress via parenting practices are discussed.