Type 2 diabetes mellitus is known to be associated with cognitive deficits; however, their extent, overlap with aging effects, and neurobiological correlates are currently unknown. We characterized neurocognitive effects in T2DM in a large cohort complemented by meta-analysis of the published literature. As compared to age, sex, and education-matched HC, T2DM was associated with marked cognitive deficits, particularly in executive functioning and processing speed. Likewise, we found that the diagnosis of T2DM was significantly associated with gray matter atrophy, primarily within the ventral striatum, cerebellum, and putamen, with reorganization of brain activity (decreased in the caudate, frontal eye fields, and premotor cortex and increased in the subgenual area, thalamus, brainstem and posterior cingulate cortex). The structural and functional changes associated with T2DM show marked overlap with the effects of aging but appear earlier, with disease duration linked to more severe neurodegeneration. The neurocognitive impact of T2DM suggests marked acceleration of normal brain aging, by approximately 24%, made worse with chronicity. As such, neuroimaging-based biomarkers may provide a valuable adjunctive measure of T2DM progression and treatment efficacy based on neurological outcomes.