Cymbopogon citratus (lemongrass) is a widely utilized medicinal and aromatic plant with a long history of traditional applications across Asia, Africa, and South America. In recent decades, scientific attention has increasingly focused on elucidating its phytochemical composition and validating its therapeutic properties through experimental and molecular studies. The present review critically synthesizes current evidence on the phytochemical constituents of C. citratus and their antimicrobial, antioxidant, and cytoprotective effects, with particular emphasis on underlying biological mechanisms and emerging biomedical relevance. Major bioactive compounds, including citral, flavonoids, phenolic acids, terpenoids, and essential oils, are discussed in relation to their roles in inhibiting pathogenic microorganisms, neutralizing oxidative stress, and maintaining cellular integrity. The review further highlights mechanistic pathways such as membrane disruption, enzyme inhibition, reactive oxygen species modulation, mitochondrial protection, and anti-inflammatory signaling. Recent advances in nanotechnology-based formulations and functional therapeutic applications are also examined. Collectively, the evidence positions C. citratus as a promising natural source for the development of antimicrobial and cytoprotective agents, supporting further translational and clinical investigations. This review synthesizes evidence from experimental, mechanistic, and translational studies published over the last two decades.