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Introduction Maternal lifestyle during pregnancy may affect the development of overweight and obesity in the child. We examined whether maternal exercise during pregnancy is associated with offspring overweight and obesity in childhood. A secondary aim was to examine whether the association is affected by the child's physical activity level. Materials and methods This study is based on data from the Norwegian Mother, Father and Child Cohort Study (MoBa), including 44 352 pregnancies and children (n = 32 304 in week 17 and n = 32 419 in week 30 in the final adjusted model). Maternal exercise during pregnancy was self‐reported in gestational weeks 17 and 30. We conducted linear and logistic regression separately for girls and boys, and outcomes were the child's body mass index (BMI) and weight status (overweight/obese) at age 7 years. We further examined the additive joint association between maternal exercise during pregnancy and the child's leisure time physical activity on weight status at age 7 years. Results In total, 12.4% of the children were classified as overweight or obese, and 1.7% as obese. The results suggest no association between maternal exercise in both gestational weeks 17 and 30 and the weight status of the child at age 7 years. The association between maternal exercise and the child's weight status at age 7 years appears not to be affected by the child's physical activity level. Conclusion Maternal exercise level during pregnancy does not appear to be associated with the child's BMI or odds of being overweight or obese in childhood.