Type 1 diabetes (T1D) is an autoimmune disease characterized by the destruction of pancreatic β cells. We show here that the protein NOD-like receptor family pyrin domain containing 1 (NLRP1) has a key role in the pathogenesis of mouse and human T1D. More specifically, downregulation of NLRP1 expression occurs during T helper 17 (Th17) differentiation, alongside greater expression of several molecules related to Th17 cell differentiation in a signal transducers and activators of transcription 3 (STAT3)-dependent pathway. These changes lead to a consequent increase in interleukin 17 (IL-17) production within the pancreas and higher incidence of diabetes in streptozotocin (STZ)-injected mice. Finally, in patients with T1D and a SNP (rs12150220) in NLRP1, there is a robust decrease in IL-17 levels in serum and in memory Th17 cells from peripheral blood mononuclear cells. Our results demonstrate that NLRP1 acts as a negative regulator of the Th17 cell polarization program, making it an interesting target for intervention during the early stages of T1D. Keywords: NLRP1; NOD mouse; STAT-3; STZ; Th17; gut microbiota; immune system; interleukin-17; rs12150220; type 1 diabetes.