This article examines the role of the South Korean government in the diplomatic normalization process between North Korea and Japan during the early 1990s, with a particular focus on the Roh Tae-woo administration’s Nordpolitik. While initially supportive of cross-recognition and improved North Korea– Japan ties as part of Nordpolitik, South Korea gradually shifted to a more cautious and restrictive posture as formal negotiations progressed. Drawing on declassified South Korean diplomatic documents, this study reveals how the South Korean government changed its policy goals and engaged in indirect interventions — most notably by employing strategic public diplomacy campaigns aimed at influencing Japanese public opinion against North Korea. These efforts included the dissemination of negative narratives concerning North Korean human rights abuses and the regime’s nuclear ambitions. Although limitations remain due to the restricted availability of diplomatic archives, the analysis demonstrates that South Korea played a critical third-party role in the North Korea–Japan normalization talks. By investigating the constraints and strategies employed by Seoul, this article offers a new perspective on trilateral diplomacy in Northeast Asia and sheds light on the domestic and international considerations underpinning South Korea’s foreign policy during the post–Cold War transition.