β-hydroxybutyrate (BHB) is the most abundant ketone body produced during ketosis, a process initiated by glucose depletion and the β-oxidation of fatty acids in hepatocytes. Traditionally recognized as an alternative energy substrate during fasting, caloric restriction, and starvation, BHB has gained attention for its diverse signaling roles in various physiological processes. This review explores the emerging therapeutic potential of BHB in the context of sarcopenia, metabolic disorders, and neurodegenerative diseases. BHB influences gene expression, lipid metabolism, and inflammation through its inhibition of Class I Histone deacetylases (HDACs) and activation of G-protein-coupled receptors (GPCRs), specifically HCAR2 and FFAR3. These actions lead to enhanced mitochondrial function, reduced oxidative stress, and regulation of inflammatory pathways, with implication for muscle maintenance, neuroprotection, and metabolic regulation. Moreover, BHB’s ability to modulate adipose tissue lipolysis and immune responses highlight its broader potential in managing chronic metabolic conditions and aging. While these findings show BHB as a promising therapeutic agent, further research is required to determine optimal dosing strategies, long-term effects, and its translational potential in clinical settings. Understanding BHB’s mechanisms will facilitate its development as a novel therapeutic strategy for multiple organ systems affected by aging and disease.