Although considerable research has been conducted on improving sustainability performance, many important questions remain. Drawing on Social Learning Theory (SLT) and Stakeholder Theory (ST), our model suggests a mechanism, Environmental Organizational Citizenship Behavior (EOCB), through which Environmental Transformational Leadership (ETL) influences Organizational Sustainability Performance (SP). In addition, employees’ Work Passion (WP) will moderate the relationship between ETL and EOCB. A total of 240 full-time employees in Saudi Arabia’s petrochemical industries submitted responses via survey questionnaires, and the proposed hypotheses were tested using hierarchical regression analysis. Results were consistent with the hypothesized conceptual scheme in that ETL indirectly impacts SP through EOCB. In the meantime, the WP of employees plays a moderating role in the relationship between ETL and EOCB as well as in the indirect effect of ETL on SP via EOCB. As a way to improve their sustainability performance, organizations must hire and nominate ETLs who can influence their employees to become aware of environmental protection and instill these values. Furthermore, employees’ passion for their work encourages them to engage in voluntary environmental behaviors. A discussion of the findings, implications, limitations, and future research avenues is included.