Glucagon, a 29-amino acid pancreatic hormone, plays a central role in glucose homeostasis through activation of the glucagon receptor (GCGR). While clinically essential for hypoglycemia rescue, its broader therapeutic applications face limitations due to challenging biophysical properties including poor solubility, strong aggregation tendency, and chemical instability, which currently require lyophilized formulations. Recent advances in peptide engineering and formulation science have enabled the development of next-generation glucagon analogs with enhanced stability and ready-to-use profiles. Moving beyond its classical role in glucose elevation, glucagon is now recognized as a multifunctional metabolic regulator influencing lipid metabolism, energy expenditure, and cardiorenal function. This expanded understanding has driven the development of innovative GCGR-targeting therapies including multi-receptor agonists such as glucagon-like peptide-1 receptor (GLP-1R)/GCGR co-agonists for metabolic disorders and advanced dual-hormone delivery systems. This review examines the evolving pharmacology of glucagon by analyzing: (1) structural optimization and formulation strategies to address physicochemical challenges, (2) innovative delivery technologies, and (3) emerging therapeutic applications in metabolic diseases. Through critical assessment of translational challenges, this work bridges molecular insights with clinical innovation in glucagon-based therapeutics.