Diabetes is associated with a higher stroke risk, and outcomes are worse in patients with diabetes who experience strokes. Identifying diabetes-related factors may uncover mechanisms that exacerbate stroke in these patients. Nicotinamide phosphoribosyltransferase (NAMPT), an adipocytokine, is the rate-limiting enzyme for nicotinamide adenine dinucleotide ⁺ synthesis in the salvage pathway. NAMPT activation protects neurons; however, its roles in glucose metabolism disorders, cerebral ischemia, and cell death are unclear. Thus, we investigated NAMPT involvement in cerebral ischemic injury under diabetic conditions in type 2 diabetic (db/db) mice subjected to middle cerebral artery occlusion/reperfusion (MCAO/R) and in primary cultured cortical neurons. After MCAO/R, dimeric NAMPT protein levels decreased in the ischemic cortex of db/db mice and in primary cortical neurons exposed to high-glucose conditions (HGC) and oxygen–glucose deprivation/reoxygenation (OGDR), which mimic diabetic stroke conditions. HGC/OGDR increased extracellular dimeric NAMPT levels in cultured cortical neurons. Intracellular activation of NAMPT with P7C3-A20, a NAMPT activator, prevented HGC/OGDR-induced reductions in cell viability and intracellular dimeric NAMPT. Furthermore, elevated extracellular dimeric NAMPT was reduced after P7C3-A20 treatment. Intracellular NAMPT activation was associated with restored SIRT1 and FoxO3a levels. These findings demonstrate that diabetic stroke intensifies neuronal damage by disrupting the intracellular NAMPT/SIRT1/FoxO3a pathway and impairing FoxO3a activity. Therefore, intracellular dimeric NAMPT activation may support neuronal survival during diabetic stroke by modulating the SIRT1/FoxO3a pathway.