Background: Combined treatment with probiotic and peanut oral immunotherapy (PPOIT) was shown to induce sustained unresponsiveness (SU) in a proof-of-concept randomized trial. Additional data on safety and long-term outcomes are needed. This study aimed to evaluate the safety and long-term effects of PPOIT in children with peanut allergy. Methods: Open-label study of 20 children aged 1-12 years with challenge-confirmed peanut allergy; all children received 18-months of PPOIT. Efficacy endpoints were desensitization, 8-week SU, and persistence of 8-week SU at 3-years post-treatment, assessed by double-blind placebo-controlled food challenge (cumulative 4950mg peanut protein). Treatment emergent adverse events and relationship to study treatment were recorded. Immunologic measures and health related quality of life (HRQL) were evaluated at screening, end-of-treatment and 3-years post-treatment. Results: Sixteen children (75%) completed treatment. By intention-to-treat analysis, 75% (15/20) achieved desensitization and 60% (12/20) achieved 8-week SU. Ten of 12 participants with SU at end-of-treatment consented to the 3-year SU challenge; 6 (60%) had persistence of SU. PPOIT was associated with significantly reduced peanut skin prick test wheal size and serum peanut specific-IgE levels at end-of-treatment, 12-months and 3-years post-treatment. There were no serious adverse events. HRQL scores improved (exceeding the Minimal Clinically Important Difference of 0.45) at 12-months post-treatment with benefit sustained at 3-years post-treatment. Conclusions: Eighteen months of PPOIT induced high rates of desensitization and SU, and SU persisted to 3-years post-treatment in a majority of initial responders. PPOIT led to long-lasting suppression of peanut sIgE and long-lasting clinically important improvement in HRQL.