Parents of autistic children experience significantly higher stress levels than other parent groups. Externalising behaviours are also observed at a higher level in autistic than nonautistic children. All parents engage in specific parenting practices to support their children. However, most parenting practices studies are with parents of neurotypical children; it is not clear which parenting practices might be helpful in supporting autistic children. Given the strong evidence of the presence of elevated levels of parenting stress in parents of autistic children, together with evidence that parenting practices can be modified, the results from this project will address an important need through focusing on the parenting practice of mindful parenting. Results from this project also extend the literature on the potential effectiveness of a modified mindfulness-based parenting program (Two Hearts Mindful Parenting Program) with parents of autistic children. This project involved three studies. The aim of Study 1 was to systematically review quantitative literature on the associations between parenting practices and externalising behaviours in autistic children. Mindful parenting was associated with fewer or lower levels of externalising behaviours and negative parenting practices (e.g., harsh punishment) were associated with higher levels of externalising behaviours. The aim of Study 2A, which was a quantitative self-report survey design, was to examine the associations between parenting stress, parenting practices, and externalising behaviours in autistic children. Parenting stress had a significant positive association with child externalising behaviours, authoritarian, and permissive parenting practices, with mindful parenting the only parenting practice that had a significant negative association with parenting stress. Parenting practices did not mediate the relationship between parenting stress and child externalising behaviours. Study 2B investigated parent program delivery preferences (e.g., modality, program length, delivery). Parents preferred morning/afternoon weekday sessions, brief sessions, not longer than two hours, delivered face-to-face in a group setting. Study 3 was a proof-of-concept study that incorporated this feedback and assessed the social validity, acceptability, feasibility, and the preliminary effects of a modified version of the Two Hearts Mindful Parenting Program on parenting practices, parenting stress, and externalising behaviours in their autistic children using a multiple baseline design. This study found a mindful parenting program to be socially valid and acceptable to parents, and effective in improving parent outcomes, including an increase in mindful parenting and decrease in parenting stress and child externalising behaviours at an individual and group level. This research informs our theoretical understanding of the associations between parenting stress and child behaviours, and links to mindful parenting. It also informs practical recommendations for implementing parenting programs that focus on supportive parenting practices, such as mindful parenting, with a focus on acceptance. Future work will ultimately support more positive outcomes for autistic children and their families by understanding supportive parenting practices from a strengths and neurodiversity-affirming perspective.