To protect the organism against autoimmunity, self-reactive effector/memory T cells (T _E/M ) are controlled by cell-intrinsic and -extrinsic regulatory mechanisms. However, how some T _E/M cells escape regulation and cause autoimmune disease is currently not understood. Here we show that blocking IL-7 receptor-α (IL-7Rα) with monoclonal antibodies in nonobese diabetic (NOD) mice prevented autoimmune diabetes and, importantly, reversed disease in new-onset diabetic mice. Surprisingly, IL-7–deprived diabetogenic T _E/M cells remained present in the treated animals but showed increased expression of the inhibitory receptor Programmed Death 1 (PD-1) and reduced IFN-γ production. Conversely, IL-7 suppressed PD-1 expression on activated T cells in vitro. Adoptive transfer experiments revealed that T _E/M cells from anti–IL-7Rα–treated mice had lost their pathogenic potential, indicating that absence of IL-7 signals induces cell-intrinsic tolerance. In addition to this mechanism, IL-7Rα blockade altered the balance of regulatory T cells and T _E/M cells, hence promoting cell-extrinsic regulation and further increasing the threshold for diabetogenic T-cell activation. Our data demonstrate that IL-7 contributes to the pathogenesis of autoimmune diabetes by enabling T _E/M cells to remain in a functionally competent state and suggest IL-7Rα blockade as a therapy for established T-cell–dependent autoimmune diseases.