Heat stress (HS) is known to cause liver injury through mechanisms involving oxidative stress and inflammation, thereby highlighting the need for effective therapeutic interventions. This study evaluated the efficacy of sprouted black quinoa extract (SBQE) in mitigating HS-induced liver injury in a rat model. SBQE was obtained through an ultrasonication-assisted ethanol–water extraction process from black quinoa germinated for 48 h. Sprague Dawley rats (male) were administered via oral gavage SBQE at doses of 200, 400, or 800 mg/kg prior to each HS exposure (40 °C for 2 h per day over a period of 8 days). Pretreatment with SBQE resulted in a dose-dependent reduction in serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, with the high dose (800 mg/kg) reducing these enzyme levels (p < 0.001 vs. HS group) and alleviating histopathological damage, including a significant decrease in hepatocyte vacuolization and inflammatory cell infiltration (histopathological scores were reduced by p < 0.001 in the 800 mg/kg SBQE group vs. HS group). SBQE also dose-dependently inhibited the accumulation of mitochondrial reactive oxygen species (mean fluorescence intensity decreased by p < 0.001 at 800 mg/kg) and the formation of malondialdehyde while restoring the activities of antioxidant enzymes such as superoxide dismutase (p < 0.01 at 800 mg/kg), catalase (p < 0.05 at 800 mg/kg), and glutathione peroxidase (p < 0.001 at 800 mg/kg), as well as replenishing glutathione levels (p < 0.001 at 800 mg/kg). Furthermore, the levels of proinflammatory cytokines (tumor necrosis factor-alpha, interleukin-6, interleukin-1β, and interleukin-18) in liver tissue were significantly reduced (with the high dose leading to p < 0.001 vs. HS group), which was associated with enhanced nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2; p < 0.05 at 800 mg/kg) and decreased phosphorylation of nuclear factor-κB p65 (NF-κB; p < 0.001 at 800 mg/kg). Additionally, the protein expression of NOD-like receptor pyrin domain-containing 3 (NLRP3) inflammasome components and markers of apoptosis were diminished. The results demonstrated that SBQE alleviated HS-induced liver injury by concurrently activating the Nrf2 antioxidant pathway and suppressing NF-κB/NLRP3 inflammasome signaling, suggesting its potential as a nutraceutical intervention for HS-related hepatotoxicity.