Being overweight or obese (overweight/obesity) or physically aggressive in childhood and adolescence can have lifelong consequences, hence are important public health problems. Identifying a relationship between these problems would assist in understanding their developmental origins. The present paper sought to review previous studies and use meta-analysis to evaluate whether there is evidence of a relationship between overweight/obesity and physical aggression in children and adolescents. A systematic search of studies that reported the effect of overweight/obesity (in the form of body mass index) on physical aggression was conducted. A total of 23 studies were identified, representing data from 255,377 participants. The results indicate that children and adolescents who are overweight or obese are more physically aggressive than their normal-weight or underweight peers. The average weighted standardized mean difference (the effect size) for aggression in overweight and obese children and adolescents compared to others was found to be 0.27 (95% confidence interval [CI₉₅]: .17–.37), and was significant ( p<.001). Gender sub-analysis indicated that higher physical aggression amongst overweight or obese compared to normal-weight or underweight peers is a slightly larger effect for boys (standardized mean difference of .35, CI₉₅: .18–.52, p<.001) than girls (standardized mean difference of .24, CI₉₅: .07–.42, p<.01). High levels of heterogeneity (94.41%) were found between study-level effect sizes. The developmental processes that may explain the association between overweight/obesity and physical aggression in children and adolescents are discussed.