Parent mediated interventions have the potential to positively influence the interactions and developmental outcomes of children with autism spectrum disorder (ASD). However, a range of factors relating to children, parents and caregivers, and study design may impact on outcomes and thus the generalizability of these interventions to the broader community. The objective of this review was to examine factors that may influence the feasibility, appropriateness, effectiveness, and generalizability of parent mediated interventions for children with ASD. We conducted a systematic review, yielding 41 articles. There was substantial variability in the intervention type, intensity, and study quality. Notably, 46 different inclusion/exclusion criteria were reported across studies including factors relating to children's development, access to other services, comorbidities, parental factors, and access to the intervention. Fifteen articles included examination of 45 different factors potentially associated with, or influencing, intervention outcomes including child (e.g., language skills, ASD severity, cognition) and parent (e.g., adherence and fidelity, education) factors. Although there is clear evidence for an increasingly sophisticated (e.g., systematic phased research for some interventions) and diverse (e.g., studies in geographical diverse contexts including low-resource communities) approach to research examining parent mediated interventions, there remains a need for improved study quality and measurement consistency in research, including a detailed examination of factors that may predict, moderate, and mediate intervention effectiveness for children and their parents. Autism Res 2019, 12: 1304–1321. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. Lay Summary: Parent mediated interventions—in which parents adapt their own behavior or deliver interventions to help their children learn—appear to be effective for some children with autism spectrum disorder. In this review, we identified a range of child, parent, and study design factors that may influence intervention outcomes and ultimately the uptake of these approaches in the community. We suggest that research in this area could be further improved by ensuring that studies include diverse groups of children and parents, and by using study designs that help to establish not only if interventions work, but for whom they work best and why.