This study explores the advancement of ethical practices and environmental sustainability in Thai banking through an in-depth case analysis of Siam Commercial Bank (SCB), the country’s first indigenous bank founded in 1907. SCB has significantly influenced ethical banking practices and sustainability initiatives. The research provides a unique comparative analysis of SCB’s ethical frameworks and sustainability policies, assessing their impact on key stakeholders, including customers, employees, the community, and the environment. Employing a qualitative case study methodology, this study utilizes secondary data from SCB’s reports and CSR documents, analyzed through thematic analysis and descriptive statistics. The findings reveal SCB’s substantial progress in aligning ethical considerations with environmental sustainability, contributing new insights into ethical decision-making processes and the balance between profit and responsibility. Recommendations are provided to enhance ethical and sustainable practices in banking, adding to the discourse on corporate responsibility, environmental stewardship, and sustainable development.