Type 2 diabetes is a heterogeneous, progressive chronic condition for which management has traditionally focused on glycaemic control and cardiovascular risk factors, rather than focusing on altering long-term disease trajectory. Increasing evidence indicates that progression and complications might be modifiable, but the absence of a core outcome set for disease modification limits trial design and intervention comparison. To address this gap, we developed a core outcome set for disease modification in type 2 diabetes through a modified Delphi process conducted according to COMET guidance. Candidate outcomes were identified from the literature and refined by an international multidisciplinary steering group comprising clinicians, researchers, and people living with type 2 diabetes. Across two Delphi rounds involving health-care professionals, researchers, and patients (round one n=233; round two n=79), agreement was reached for 35 outcomes spanning 11 domains. This framework aims to support outcome selection, consistency across trials, comparison of interventions, and evaluation of disease-modifying strategies in type 2 diabetes.