<jats:title>Abstract</jats:title> <jats:p>Obesity-induced NLRP3 inflammasome hyperactivation is a major risk factor for human diseases spanning autoimmune, degenerative, metabolic disorders, and cancer. However, its underlying mechanisms remain elusive. Here we show that obesity compromises the function of SAMHD1 – an evolutionarily-conserved deoxyribonucleotide triphosphate (dNTP) hydrolase essential for cellular nucleotide homeostasis. This dysregulation leads to aberrant accumulation of cytosolic dNTPs in macrophages, which are subsequently transported into mitochondria, and directly serve as building blocks for new mitochondrial DNA (mtDNA) synthesis bypassing the CMPK2-mediated nucleotide salvage synthesis pathway. The uncontrolled mtDNA neosythesis then triggers the overproduction of oxidized mtDNA upon NLRP3 activators stimulation, ultimately resulting in hyperactivation of NLRP3 inflammasome. Genetic ablation of mouse Samhd1 leads to overwhelmed NLRP3 inflammasome activation in vivo and exacerbates immunopathology in multiple NLRP3-dependent disease models. Moreover, mice lacking SAMHD1 exhibit heightened circulating IL-1β, insulin resistance, and metabolic dysfunction-associated steatohepatitis (MASH) upon high-fat diet feeding. Overall, our study establishes SAMHD1 as a macrophage-intrinsic valve restraining NLRP3 inflammasome activation, illuminating that obesity, through compromising SAMHD1's function, rewires macrophage nucleotide metabolism to enable hyperinflammation and disease development.</jats:p>