Socioeconomic status has been found to be a significant predictor of quality of life, with individuals of higher socioeconomic status reporting better quality of life. However, social capital may play a mediating role in this relationship. This study highlights the need for further research on the role of social capital in the relationship between socioeconomic status and quality of life, and the potential implications for policies aimed at reducing health and social inequalities. The study used a cross-sectional design with 1792 adults 18 and older from Wave 2 of the Study of Global AGEing and Adult Health. We employed a mediation analysis to investigate the relationship between socioeconomic status, social capital, and quality of life. The results showed that socioeconomic status was a strong predictor of social capital and quality of life. In addition to this, there was a positive correlation between social capital and quality of life. We found social capital to be a significant mechanism by which adults’ socioeconomic status influences their quality of life. It is crucial to invest in social infrastructure, encourage social cohesiveness, and decrease social inequities due to the significance of social capital in the connection between socioeconomic status and quality of life. To improve quality of life, policymakers and practitioners might concentrate on creating and fostering social networks and connections in communities, encouraging social capital among people, and ensuring fair access to resources and opportunities.