AimsThe global historical and projected health impacts of the escalating burden of obesity on young adults, who are particularly susceptible to weight gain during transitional life stages, remain insufficiently understood.Materials and MethodsUsing data from the Global Burden of Disease Study 2019, we analysed the disability‐adjusted life‐years (DALYs) and deaths attributable to high body mass index (BMI) among young adults aged 20–44 years globally and by age, sex, year, location and disease between 1990 and 2019. Future projections until 2050 were further assessed.ResultsThe global burden for young adults attributable to high BMI more than doubled from 1990 to 2019, reaching 24,509.8 (95% uncertainty interval [UI] 20,191.8–28,966.0) thousand for DALYs and 321.9 (258.3–384.2) thousand for deaths. Males had a higher burden and faster increase than females. The burden escalated with advancing age. From 1990 to 2019, regions with middle Socio‐demographic Index (SDI) replaced regions with high‐middle SDI to have the highest age‐standardized rates of DALYs and deaths, while regions with low‐middle SDI witnessed the largest rise. Stroke, ischaemic heart disease and diabetes mellitus were consistently the top three causes of high BMI‐related burden, together accounting for 74.7% (70.8–78.4) for DALYs and 81.2% (77.6–84.2) for deaths in 2019. By 2050, the age‐standardized rates of DALYs due to high BMI tripled that in 1990, with the corresponding rates for deaths expected to double. Among the 10 most populous countries, India was projected to have the highest rates and the fastest increase in both DALYs and deaths by 2050.ConclusionsThe escalating disease burden attributable to high BMI in young adults, marked by notable demographic and geographic variations, highlights the urgent need for tailored public health interventions on weight management during young adulthood.