Most studies on the association of in utero exposure to cigarette smoking and childhood overweight or obesity (OWO) were based on maternal self-reported smoking data and few were based on objective biomarkers. In this study, we evaluated the associations between self-reported and biomarkers of in utero exposure to cigarette smoking with risk of childhood OWO. We analyzed data from 2351 mother-child pairs in the Boston Birth Cohort, a US low-income minority cohort that enrolled children at birth and followed prospectively up to age 18 years. In utero smoking exposure was measured by maternal self-report and by maternal and cord plasma cotinine and hydroxycotinine metabolites. We assessed the individual and joint associations of each smoking exposure measure and maternal OWO with childhood OWO using multinomial logistic regressions. We used nested logistic regressions to investigate the childhood OWO prediction performance when adding maternal and cord plasma biomarkers as input covariates on top of self-reported data. Our results demonstrated that in utero cigarette smoking exposure defined by self-report and by maternal or cord metabolites were consistently associated with increased risk of long-term child OWO. Adding maternal and cord plasma biomarker information to self-reported data improved the prediction accuracy of long-term child OWO risk.