Artificial sweeteners are used to reduce energy intake, but studies suggest that consumption during pregnancy may impact the offspring’s risk of overweight. In this longitudinal cohort study, we aimed to examine the association between consumption of artificially sweetened or sugar-sweetened beverages during pregnancy and offspring overweight from birth to 18 years in the Danish National Birth Cohort (DNBC). 101,042 pregnancies were enrolled in the DNBC from 1996-2002. Follow-up was conducted throughout pregnancy, childhood, and adolescence. 72,821 women completed a Food Frequency Questionnaire during pregnancy reporting intake of beverages sweetened with artificial sweeteners or sugar. Offspring height and weight were obtained during childhood and adolescence. Multivariate logistic regression was performed to estimate the odds ratio (OR) for overweight concerning maternal beverage consumption. Analyses were adjusted for risk factors for childhood overweight, including maternal age, pre-pregnancy body mass index (BMI), physical activity and smoking in pregnancy, healthy eating index, paternal BMI, socioeconomic status, and duration of breastfeeding. We found increased odds of overweight in 7, 11, 14, and 18-year-old offspring, whose mothers reported drinking ≥1 artificially sweetened beverages daily during pregnancy compared to no consumption (18 years: adjusted OR 1.26 (95% confidence interval 1.12, 1.42)). We found decreased adjusted odds of overweight in 11 and 18-year-old offspring, whose mothers reported drinking ≥1 sugar-sweetened beverages daily during pregnancy compared to no consumption. We found that consumption of artificially sweetened beverages during pregnancy was associated with an increased risk of overweight in childhood and adolescence. Adjustment for risk factors for overweight and total energy intake did not explain the association. Further studies are warranted to establish the mechanism of the association.