Sports diplomacy has become one of the key instruments of soft power for countries in international relations in recent decades; however, the role of global good governance in strengthening or weakening the effectiveness of this tool has received limited theoretical and empirical scrutiny. The primary objective of this study was to examine the impact of global good governance on the functioning of sports diplomacy within the framework of soft power. This research adopted a qualitative approach with a comparative case study design, analyzing two major events—the 2008 Beijing Olympics and the 2018 FIFA World Cup in Russia—based on Joseph Nye’s theoretical framework of soft power. Data were collected from official documents of international institutions, monitoring reports, and credible academic sources, and analyzed using thematic analysis. The findings revealed that sports diplomacy in both events performed relatively successfully in the dimension of “cultural and symbolic attractiveness” of soft power; however, weaknesses in aspects of good governance—particularly transparency, accountability, and respect for fundamental rights—undermined the sustainability and international credibility of these achievements. The comparative results between China and Russia indicate that soft power generated through sports diplomacy, in the absence of good governance, tends to have a short-term and predominantly domestic function rather than leading to lasting influence in the international system.