Background: Japan and South Korea, two advanced East Asian nations with universal health coverage and similar demographic challenges, have developed markedly different emergency medical services (EMS) systems. Despite growing interest in international benchmarking, structured, comparative studies that yield policy-relevant insights remain limited. Methods: We conducted a multisource comparative health-systems analysis using statutory laws, government publications, academic society reports, peer-reviewed literature, and national statistics. Key domains included EMS governance, workforce, prehospital organization, hospital-based emergency care, legal obligations for EMS patient transport and hospital acceptance, and governance and quality assurance mechanisms. Data were synthesized in comparative tables and narrative summaries to highlight structural and operational differences. Results: Japan’s EMS system operates under decentralized municipal control through 722 fire departments, serving 4,100 designated emergency institutions with 6,139 board-certified emergency physicians. In 2023, over 6.64 million ambulance dispatches occurred, and 8.6% were classified as critical cases (1.3% death and 7.3% severe). Korea’s EMS system is centrally governed with 412 designated facilities in a tiered system and 2,464 specialists. Annual ambulance activations exceeded 3.5 million, with severe cases accounting for approximately 5% to 10%. Japan employs a multilayered legal–institutional structure, primarily involving the Fire Service Act and the Medical Practitioners Act, allowing clinical discretion, whereas Korea enforces unified regulations with stricter obligations and criminal penalties for hospital refusal of emergency patients. Conclusion The contrasting systems suggest that hybrid governance that combines centralized standard settings with local operational flexibility may optimize EMS performance. These findings provide lessons for EMS reform, cross-border collaboration, and disaster preparedness in high-income nations facing similar demographic and healthcare challenges.