This study analyzed the effect of tertius iungens orientation on individual job performance through knowledge-sharing activities in social media environments. To this end, factors influencing social media knowledge-sharing activities and tertius iungens orientation were derived from a comprehensive perspective that includes both individual and social factors. Based on social cognitive theory and social capital theory, self-efficacy and enjoyment of helping were proposed as individual factors, and social interaction ties and norms of reciprocity were proposed as social factors. To test the research model proposed in this study, data were collected from 234 office workers, and the research model was empirically tested through structural equation modeling. The analysis results showed that self-efficacy, social interaction ties, and norms of reciprocity had positive effects on tertius iungens orientation and social media knowledge-sharing activities. Furthermore, social media knowledge-sharing activities were shown to have a positive relationship with individual job performance. Based on the empirical analysis results, the findings of the study were discussed, and theoretical and practical implications along with research limitations were presented.