While inflammatory mechanisms driving hepatocellular carcinoma (HCC) had been proposed, the regulators of anti-cancer immunity in HCC remain poorly understood. We found that IL-27 receptor (IL-27R) signaling promotes HCC development in vivo. High IL-27EBI3 cytokine or IL-27RA expression correlated with poor prognosis for patients with HCC. Loss of IL-27R suppressed HCC in vivo in two different models of hepatocarcinogenesis. Mechanistically, IL-27R signaling within the tumor microenvironment restrains the cytotoxicity of innate cytotoxic lymphocytes. IL-27R ablation enhanced their accumulation and activation, while depletion or functional impairment of innate cytotoxic cells abrogated the effect of IL-27R disruption. Pharmacological neutralization of IL-27 signaling increased infiltration of innate cytotoxic lymphocytes with upregulated cytotoxic molecules and reduced HCC development. Our data reveal an unexpected role of IL-27R signaling as an immunological checkpoint regulating innate cytotoxic lymphocytes and promoting HCC of different etiologies, thus indicating a therapeutic potential for IL-27 pathway blockade in HCC.