Aims: Gestational diabetes mellitus (GDM) is one of the most common pregnancy complications, and though it may be linked to childhood adversity, the effect of different types of adversity remains unclear. Childhood adversity is linked to a younger maternal age, which may hide the overall impact of adversity on GDM risk. We therefore aimed to explore the association between different types of childhood adversity and GDM while accounting for the potential impact of maternal age. Methods: We used Danish nation-wide register data, including 208,207 women giving birth for the first time from 2004 to 2018. Five adversity groups were used to examine the effect of childhood adversity on GDM risk: (1) low (referent group), (2) early life material deprivation, (3) persistent deprivation, (4) loss or threat of loss within the family and (5) high adversity. Results: 5375 women were diagnosed with GDM in the study population (2.6% absolute risk). Compared to women who experienced low adversity, the other adversity groups had a higher GDM risk (absolute difference [%]) directly; early material deprivation (0.64% [95% CI 0.44; 0.84]), persistent deprivation (0.63% [0.41; 0.86]), loss or threat of loss (0.73% [0.42; 1.05]) and high adversity (0.80% [0.32; 1.27]). The indirect effect of maternal age attenuated the total effect of childhood adversity on GDM by an absolute difference of 0.25%–0.46%. Conclusions: Experiencing childhood adversity to any extent is associated with a higher risk of GDM. Interventions aimed at preventing childhood adversity may have a positive effect in reducing GDM burden and the associated health risks.