Introduction: In 2008, a conceptual model explaining the role of motor competence (MC) in children’s physical activity (PA), weight status, perceived MC and health-related fitness was published.Objective: The purpose of the current review was to systematically compile mediation, longitudinal and experimental evidence in support of this conceptual model.Methods: This systematic review (registered with PROSPERO on 28 April 2020) was conducted in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) statement. Separate searches were undertaken for each pathway of interest (final search 8 November 2019) using CINAHL Complete, ERIC, Medline (OVID), PsycINFO, Web of Science Core Collection, Scopus and SportDiscus. Potential articles were initially identified through abstract and title checking (N = 585) then screened further and combined into one review (n = 152), with 43 articles identified for extraction. Studies needed to be original and peer reviewed, include typically developing children and adolescents first assessed between 2 and 18 years and objective assessment of gross MC and at least one other variable (i.e., PA, weight status, perceived MC, health-related fitness). PA included sport participation, but sport-specific samples were excluded. Longitudinal or experimental designs and cross-sectional mediated models were sought. Strength of evidence was calculated for each pathway in both directions for each domain (i.e., skill composite, object control and locomotor/coordination/stability) by dividing the proportion of studies indicating a significantly positive pathway in the hypothesised direction by the total associations examined for that pathway. Classifications were no association (0–33%), indeterminate/inconsistent (34–59%), or a positive ‘+’ or negative ‘ − ’ association (≥ 60%). The latter category was classified as strong evidence (i.e., ++or −−) when four or more studies found an association. If the total number of studies in a domain of interest was three or fewer, this was considered insufficient evidence to make a determination.Results: There was strong evidence in both directions for a negative association between MC and weight status. There was strong positive evidence for a pathway from MC to fitness and indeterminate evidence for the reverse. There was indeterminate evidence for a pathway from MC to PA and no evidence for the reverse pathway. There was insufficient evidence for the MC to perceived MC pathway. There was strong positive evidence for the fitness-mediated MC/PA pathway in both directions. There was indeterminate evidence for the perceived MC-mediated pathway from PA to MC and no evidence for the reverse.Conclusion: Bidirectional longitudinal associations of MC with weight status are consistent with the model authored by Stodden et al. (Quest 2008;60(2):290–306, 2008). However, to test the whole model, the field needs robust longitudinal studies across childhood and adolescence that include all variables in the model, have multiple time points and account for potential confounding factors. Furthermore, experimental studies that examine change in MC relative to change in the other constructs are needed.Trial Registrations: PROSPERO ID# CRD42020155799.