Interleukin-2 (IL-2) is a critical cytokine for the homeostasis and function of forkhead box p3-expressing regulatory T cells (Foxp3(+)Tregs). Dysregulation of the IL-2-IL-2 receptor axis is associated with aberrant Foxp3(+)Tregs and T cell-mediated autoimmune diseases such as type 1 diabetes. Treatment with recombinant IL-2 has been reported to enhance Foxp3(+)Tregs and suppress different models of autoimmunity. However, efficacy of IL-2 therapy is dependent on achieving sufficient levels of IL-2 to boost tissue-resident Foxp3(+)Tregs while avoiding the potential toxic effects of systemic IL-2. With this in mind, adeno-associated virus (AAV) vector gene delivery was used to localize IL-2 expression to the islets of NOD mice. Injection of a double-stranded AAV vector encoding IL-2 driven by a mouse insulin promoter (dsAAVmIP-IL2) increased Foxp3(+)Tregs in the islets but not the draining pancreatic lymph nodes. Islet Foxp3(+)Tregs in dsAAVmIP-IL2-treated NOD mice exhibited enhanced fitness marked by increased expression of Bcl-2, proliferation, and suppressor function. In contrast, ectopic IL-2 had no significant effect on conventional islet-infiltrating effector T cells. Notably, β-cell-specific IL-2 expression suppressed late preclinical type 1 diabetes in NOD mice. Collectively, these findings demonstrate that β-cell-specific IL-2 expands an islet-resident Foxp3(+)Tregs pool that effectively suppresses ongoing type 1 diabetes long term.