We aimed to assess the relationships between early-life tobacco smoke exposures and the incident risk of type 2 diabetes (T2D) in later life as well as the joint effects and interactions between genetic susceptibility and early-life tobacco exposures.We used data on in utero tobacco exposure and the age of smoking initiation to estimate the status of early-life tobacco exposure in the UK Biobank. Cox proportion hazard models were applied to estimate the associations between early-life tobacco exposure and T2D risk and investigate joint effects and interactions of early-life tobacco smoke exposure with genetic susceptibility.Among 407,943 subjects from the UK Biobank, 17,115 incident cases were documented during a median follow-up of 12.80 years. Compared with subjects without prenatal tobacco exposure, those with in utero tobacco exposure had a higher risk of T2D with a hazard ratio (HR) (95 % confidence interval [CI]) of 1.11 (1.08, 1.15). Besides, the HRs (95 % CIs) of incident T2D for smoking initiation in adulthood, adolescence, and childhood (vs. never smokers) were 1.36 (1.31, 1.42), 1.44 (1.38, 1.50), and 1.78 (1.69, 1.88), respectively (P trend <0.001). No interaction between early-life tobacco exposure and genetic susceptibility was observed. In addition, participants with prenatal (HR 4.67 [95 % CI 4.31, 5.06]) or childhood (6.91 [6.18, 7.72]) tobacco exposure combined with high genetic risk showed the highest risk of T2D, compared to low genetic risk subjects without early-life smoke exposure.Early-life tobacco exposure was associated with an increased risk of T2D later in life regardless of genetic background. This highlights the significance of education campaigns aimed at reducing smoking among children, adolescents, and pregnant women as an effective measure to combat the T2D epidemic.Copyright © 2023 Elsevier B.V. All rights reserved.