Streptococcus anginosus (S. anginosus, SA), a facultatively anaerobic coccus, functions as both a commensal bacterium and an opportunistic pathogen. It is frequently associated with localized suppurative infections and abscess formation. Increasing evidence implicates it as an emerging pathogen that can trigger gastritis and gastric cancer. This review synthesizes current knowledge with emphasis on pathogenic mechanisms of infections and gastric cancer, as well as clinical management. Pathogenic mechanisms include bacterial adhesion, microbe-host interactions, immune microenvironment remodeling, candidate metabolites and extracellular vesicles as potential mediators. We further explore its possible involvement in the oral-gastric axis and niche adaptation, as well as antimicrobial resistance. Current and emerging diagnostic, therapeutic and preventive strategies targeting S. anginosus are systematically evaluated. This review highlights the context-dependent pathogenicity of S. anginosus and its ecological interactions, providing a critical foundation for the development of robust diagnostic biomarkers and precision therapeutic strategies.