The pursuit of sustainable development has become a global priority, with the United Nations Sustainable Development Goals (UN SDGs) serving as a comprehensive framework for addressing various social, economic, and environmental challenges. Employing the stimulus–organization–response (SOR) model, this study examines the impact of customer’s perceptions of the firm’s compliance with the SDGs on customers’ perceptions and loyalty through the mediation roles of image, trust, and reputation in the customer’s evaluation of the firm in the banking sector in Turkey. To achieve these objectives, a quantitative research approach was used, and 455 valid responses were collected from retail banking customers through an online survey. Data from the study were statistically analyzed using partial least-squares–structural equation modeling (PLS-SEM). The findings reveal significant positive relationships between SDG implementation and customers’ perceptions of banking institutions’ image, trust, and reputation. Furthermore, favorable image, trust, and favorable reputation are found to positively influence customer loyalty in the banking sector. The mediation analyses confirm that each of the mediating variables partially mediates the relationships between SDG implementation and customer loyalty, underscoring the significance of these intermediate variables in shaping customers’ loyalty behaviors. This research contributes to both theoretical and practical domains by providing insights into the role of SDG implementation in enhancing customer perceptions and loyalty in the banking sector. Managerial implications are discussed, and recommendations are provided for banking institutions seeking to leverage the SDGs to strengthen customer relationships and achieve sustainable growth.