<p>This study examines how CRDB Bank Plc and NMB Bank Plc in Tanzania integrate environmental, social, and governance (ESG) principles and align their operations with the Sustainable Development Goals (SDGs). Using a qualitative comparative case study of annual reports, sustainability disclosures, and bond frameworks, triangulated with third-party evaluations and academic literature, the analysis identifies contrasting but complementary pathways. CRDB has pursued a finance-led, climate-focused trajectory, leveraging its accreditation with the Green Climate Fund and pioneering green bonds to mobilize capital for renewable energy, agriculture, and infrastructure. NMB, by contrast, has advanced a socially inclusive model, channeling sustainability bond proceeds into education, healthcare, gender equality, and reforestation. Three key enablers emerge: board-level leadership, international partnerships, and supportive but non-binding policies. Persistent challenges include limited technical capacity, the absence of standardized ESG metrics, and trade-offs between profitability and sustainability. Theoretically, the study enriches debates on the CSR-to-ESG transition and institutional entrepreneurship in frontier markets. Practically, it offers lessons for banks, regulators, and investors on aligning global frameworks with local priorities, showing that even without binding regulation, financial institutions can act as catalysts of inclusive, climate-resilient growth.</p>