Background/objectives: A number of meta-analyses suggest an association between any maternal smoking in pregnancy and offspring overweight obesity. Whether there is a dose–response relationship across number of cigarettes and whether this differs by sex remains unclear. Subject/methods: Studies reporting number of cigarettes smoked during pregnancy and offspring BMI published up to May 2015 were searched. An individual patient data meta-analysis of association between the number of cigarettes smoked during pregnancy and offspring overweight (defined according to the International Obesity Task Force reference) was computed using a generalized additive mixed model with non-linear effects and adjustment for confounders (maternal weight status, breastfeeding, and maternal education) and stratification for sex. Results: Of 26 identified studies, 16 authors provided data on a total of 238,340 mother–child-pairs. A linear positive association was observed between the number of cigarettes smoked and offspring overweight for up to 15 cigarettes per day with an OR increase per cigarette of 1.03, 95% CI = [1.02–1.03]. The OR flattened with higher cigarette use. Associations were similar in males and females. Sensitivity analyses supported these results. Conclusions: A linear dose–response relationship of maternal smoking was observed in the range of 1–15 cigarettes per day equally in boys and girls with no further risk increase for doses above 15 cigarettes.