Necroptosis is an inflammatory form of programmed cell death that originated as a pathogen defence mechanism. During bacterial and viral infections, the necroptotic executioner protein, MLKL, has been identified as both a protector against- and progressor of- infection. Across the globe, 2-3% of humans carry a single nucleotide polymorphism, Ser132Pro, in MLKL that confers a gain in necroptotic function. In human cells this is detected under pharmacological and regulatory inhibition. In mouse cells is detected as an enhanced sensitivity to IFN- β induced death. In a CRISPR-Cas9 generated mouse model, MlklS131P, we observed that this gain-of-function mutation manifests in vivo changes to the immune response, defective emergency haematopoiesis, and impaired bacterial clearance. At steady state, MlklS131P homozygotes present with significant reductions in the inflammatory monocyte population in the bone marrow. Following myelosuppressive irradiation or during competitive bone marrow transplants, a broader hematopoietic defect is observed across all immune cells. This MlklS131P driven hematopoietic dysfunction results in defective mobilisation of innate and adaptive immune cells under inflammatory conditions. Specifically, we show that MlklS131P homozygosity reduces the capacity to clear Salmonella during infection, with the increased bacterial burdens present in the spleen and liver accompanied by reduced quantities of peripheral lymphocytes and monocytes. Collectively, these findings indicate mutations that alter MLKL function can disrupt the integral inflammatory and immune responses thus, raising important questions as to health implications for the proportion of the population that are carriers.