The innate immune system wields an arsenal of pattern-recognition receptors (PRRs) to detect cellular danger signals including pathogens and sterile injury. Upon activation, a subset of intracellular PRRs assemble into multiprotein complexes called inflammasomes. These signaling complexes mature inflammatory cytokines and execute a form of lytic cell death known as pyroptosis. This cascade is tightly regulated with multiple checkpoints to prevent aberrant activation and associated autoinflammatory diseases. NLRP1 and CARD8 are related inflammasome forming proteins with shared domain architectures. Both proteins undergo self-cleavage to generate inhibitory N-terminal (NT) and inflammatory C-terminal (CT) fragments that remain associated and autoinhibited. CT release is sufficient for activation. While the endogenous danger signal detected by NLRP1 and CARD8 remains to be discovered, inhibition of the serine hydrolases, dipeptidyl peptidases 8 and 9 (DPP8/9), activates both inflammasomes. Here we demonstrate that DPP8/9 gate pyroptosis via two distinct mechanisms. One checkpoint depends on the canonical catalytic activity of DPP8/9. Using novel chemoproteomic techniques we show DPP8/9 preferentially cleave proline containing peptides. Ablation of this activity accelerates the rate of proteosome-mediated NT degradation releasing CT fragments to form an inflammasome. The second checkpoint relies on the surprising affinity of DPP8/9 for NLRP1 and CARD8. Cryo-EM structures of these complexes revealed that DPP8/9 directly sequester NLRP1-CT and CARD-CT. Binding is necessary for inflammasome regulation and potent inhibitors of DPP8/9 disrupt complex formation. Overall, this work reveals the mechanistic basis for how DPP8/9 inhibition promotes pyroptosis and suggests strategies to pharmacological modulate these inflammasomes.