Early-onset type 2 diabetes (defined as type 2 diabetes diagnosed in people aged <40 years) is an increasingly prevalent condition with a more aggressive disease trajectory than late-onset type 2 diabetes. It is associated with accelerated microvascular and macrovascular complications, reduced life expectancy, and adverse pregnancy outcomes. Despite its rising incidence, global management strategies have mostly been extrapolated from studies in older adults with limited evidence specific to younger populations. In this Series paper, we aim to highlight the unique challenges in the management of early-onset type 2 diabetes and why current models of care are inadequate. We emphasise that early-onset type 2 diabetes necessitates proactive and combination treatment strategies to address weight, faster β-cell decline, worse insulin resistance, and rapidly progressing hyperglycaemia compared with late-onset type 2 diabetes. However, there is minimal evidence on how best to address these factors and clinical inertia risks contributing to glycaemic burden. Cardiovascular risk assessment tools underestimate long-term risk, contributing to low use of statin and antihypertensive therapy. Reproductive health remains a key concern, yet preconception and pregnancy care are inadequate, with low adherence to recommended interventions. Health-care systems are not optimised to address the distinct needs of young adults, and gaps in transitional care (from paediatric to adult services) contribute to disengagement and adverse outcomes. Addressing these challenges requires tailored management strategies that consider the unique metabolic and psychosocial factors in this population. In this Series paper, we summarise the evidence base for the management of early-onset type 2 diabetes, key evidence gaps, and discuss the multisectoral and transdisciplinary elements needed to achieve population-level prevention to reverse these concerning trends.