Background/Objectives: Metabolic-dysfunction-associated steatotic liver disease (MASLD) and metabolic-dysfunction-associated steatohepatitis (MASH) arise in the setting of obesity, insulin resistance, type 2 diabetes, and metabolic syndrome. This review examines how mitochondrial dysfunction participates in the transition from lipid accumulation to hepatocyte injury, inflammation, and fibrosis, and how evidence from human, animal, and in vitro studies should be interpreted. Methods: We provide a narrative synthesis of mechanistic, translational, and clinical studies on hepatic mitochondrial metabolism, fatty acid oxidation, oxidative phosphorylation, redox stress, organelle crosstalk, mitophagy, mitochondrial biogenesis and proteostasis, mitochondrial danger signals, the gut-liver-mitochondria axis, and mitochondria-related therapeutic strategies. Results: In early metabolic overload, mitochondrial oxidation may increase as an adaptive response. With persistent substrate pressure, this adaptation can become inefficient, with impaired fatty acid disposal, less efficient oxidative phosphorylation, reactive oxygen species production, redox imbalance, defective mitochondrial quality control, altered mitochondrial biogenesis, mitochondrial unfolded protein response (UPRmt)-related proteostatic stress and mtDNA instability. Mitochondrial DNA and RNA released from damaged organelles may also activate cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING), inflammasome, and RNA-sensing pathways, linking hepatocyte stress to macrophage activation, stellate cell activation, extracellular matrix deposition, and fibrosis. Conclusions: The current evidence supports mitochondria as a stage-dependent amplifier of metabolic liver injury rather than a uniform initiating event. Clinically, the strongest evidence remains with upstream metabolic unloading and liver-directed metabolic therapy, whereas direct mitochondrial restoration and quality-control targeting remain promising but less mature.