Elaeocarpus sylvestris (Lour.) Poir., an evergreen tree native to East and Southeast Asia, has gained increasing scientific attention owing to its broad pharmacological properties. Traditionally used in East Asian medicine to treat inflammation, fever, and infectious diseases, modern research has revealed diverse bioactivities, including potent antioxidant, anti-inflammatory, antiviral, anticancer, antidiabetic, and immunomodulatory effects. This therapeutic potential is primarily attributed to its rich phytochemical composition, particularly polyphenols such as geraniin, 1,2,3,4,6-penta-O-galloyl-β-D-glucose and quercetin. This review particularly focuses on the chemistry of E. sylvestris, summarizing structurally elucidated compounds, including hydrolysable tannins, flavonoids, and triterpenoids, along with recent insights into the structure–activity relationships that underpin these antiviral, antioxidant, and anticancer activities. Recent studies have demonstrated substantial antiviral efficacy of E. sylvestris extracts and isolated compounds against major human pathogens, including herpesviruses, influenza A virus, and SARS-CoV-2, supported by in silico, in vitro, in vivo, and early-phase clinical evaluations. Its cosmeceutical applications, including antioxidant, skin-whitening, and blue-light protective effects, further highlight its multifunctional potential. To our knowledge, this is the first comprehensive review summarizing the phytochemistry, pharmacological activities, therapeutic potential, and cosmeceutical applications of E. sylvestris. Despite these promising findings, challenges remain in elucidating precise molecular mechanisms, pharmacokinetics, and clinical validation. This review identifies current research gaps and future directions necessary to advance E. sylvestris as a scientifically validated natural therapeutic resource.