Pig islets are an alternative source for islet transplantation to treat type 1 diabetes (T1D), but reproducible curative potential in the pig‐to‐nonhuman primate (NHP) model has not been demonstrated. Here, we report that pig islet grafts survived and maintained normoglycemia for >6 months in four of five consecutive immunosuppressed NHPs. Pig islets were isolated from designated pathogen‐free (DPF) miniature pigs and infused intraportally into streptozotocin‐induced diabetic rhesus monkeys under pretreatment with cobra venom factor (CVF), anti‐thymocyte globulin (ATG) induction and maintenance with anti‐CD154 monoclonal antibody and low‐dose sirolimus. Ex vivo expanded autologous regulatory T cells were adoptively transferred in three recipients. Blood glucose levels were promptly normalized in all five monkeys and normoglycemia (90–110 mg/dL) was maintained for >6 months in four cases, the longest currently up to 603 days. Intravenous glucose tolerance tests during the follow‐up period showed excellent glucose disposal capacity and porcine C‐peptide responses. Adoptive transfer of autologous regulatory T cells was likely to be associated with more stable and durable normoglycemia. Importantly, the recipients showed no serious adverse effects. Taken together, our results confirm the clinical feasibility of pig islet transplantation to treat T1D patients without the need for excessive immunosuppressive therapy. The authors report control of diabetes for longer than six months in four consecutive nonhuman primates by the transplantation of adult pig islets using a modest immunosuppressive regimen with an acceptable adverse effect profile.