Situational leadership theory and the contingency approach of leadership were utilized and applied based on situational theory. Based on a total of four foundational theories, that is, bottom-up spillover theory, theories of prosocial behavior, and so on, this study empirically analyzed what influence a chief executive officer’s (CEO’s) sustainable leadership styles (servant, ethical, and authentic leadership) have on the psychological well-being and organizational citizenship behaviors of organization members. The study was conducted on adult employees of midsized or larger companies (including subsidiaries) across four countries: South Korea, the United Kingdom, the United States, and South Africa. Data were obtained from 649 adult employees. SmartPLS was used to conduct structural equation modeling analysis of the data. The results were as follows: (1) CEOs’ servant and authentic leadership styles had statistically significant positive (+) effects on employees’ psychological well-being; however, ethical leadership did not. (2) CEOs’ ethical leadership had a statistically significant (+) effect on employees’ organizational citizenship behavior; however, servant and authentic leadership did not. (3) Employees’ psychological well-being had a statistically significant (+) effect on organizational citizenship behavior. CEOs are attracting more attention than ever, leading companies in today’s rapidly changing times. This suggests that it is necessary to comprehend principles that show when, where, and how important leaders are and sustainable leadership styles that can increase their chances of success. Moreover, this study derived constructive implications that a leader can overcome today’s challenges through sustainable leadership styles.