In response to microbes and other danger signals, the NLRP3 inflammasome in immune cells triggers the activation of the protease caspase-1, which mediates the maturation of the inflammatory cytokine IL-1β. Here, we investigated how the NLRP3 inflammasome is regulated. We found that its activation in primary mouse macrophages induced the Src family kinase Lyn to phosphorylate NLRP3 at Tyr918, which correlated with a subsequent increase in its ubiquitination that facilitated its proteasome-mediated degradation. NLRP3 tyrosine phosphorylation and ubiquitination was abrogated in Lyn-deficient macrophages, which produced increased amounts of IL-1β. Furthermore, mice lacking Lyn were more susceptible to LPS-induced septic shock in an NLRP3-dependent manner. Our data demonstrate that Lyn-mediated tyrosine phosphorylation is a prerequisite for the ubiquitination that dampens NLRP3 inflammasome activity.