Background: Caesarean section birth may be associated with overweight in childhood; however, findings to date have been inconsistent. This study explored the association of caesarean section vs. vaginal birth with childhood overweight in Vietnam. Methods: This longitudinal cohort study explored the association of delivery mode with overweight, obesity, and overweight/or obesity at 8 years of age in children (n = 1937) across 20 sites in Vietnam, using Young Lives longitudinal cohort study data. Categories were defined using BMI z-scores in relationship to the World Health Organization (WHO) reference median: overweight >1 and <2 standard deviations (SD) above WHO reference median, obese >2 SD, and overweight/or obese >1 SD. Individual questionnaire data collected sociodemographic information and pregnancy/birth information through face-to-face interviews with mothers/caregivers. Anthropometric measurements for mother and child were collected at baseline and at 8 years for children. Results: Adjusted multivariable logistic models revealed a twofold increase in odds at age 8 years of overweight [odds ratio (OR) = 1.8, 95% confidence interval (95% CI) 1.03-3.2, p = 0.039], obese (OR = 2.2, 95% CI 1.2-4.0, p = 0.014), or overweight/or obese (OR = 2.1, 95% CI 1.3-3.3, p = 0.002) for children born through caesarean section compared with vaginal birth. Children born through planned caesarean section (adjusted OR = 2.3, 95% CI 1.2-4.1, p < 0.001) and unplanned caesarean section (adjusted OR = 1.9, 95% CI 1.1-3.5, p = 0.03) had similar increased odds of overweight/or obesity compared with children born through vaginal birth. Conclusions: These findings suggest that there may be an association between caesarean section and childhood overweight even after adjustment for confounders. Further research is needed to explore the underlying mechanisms of this finding.