As environmental and social concerns reshape global capital markets, investors increasingly prioritize sustainable practices alongside financial returns. This paper examines the relationship between environmental sustainability, innovation, and corporate financial performance in the Greek and broader European context. The ATHEX ESG Index, part of the Athens Stock Exchange’s sustainability framework, serves as a benchmark to identify firms that meet environmental, social, and governance (ESG) criteria. Utilizing the abovementioned index as a benchmark, we analyze both the composition of ESG-compliant firms and the evolution of the index from 2021 to 2024. We combine index performance data with integrated financial reports from a selected sample of Greek companies based on sectoral relevance and data availability to construct a panel dataset. Through econometric modeling and content analysis, we identified a significant positive association between firms’ sustainability-driven innovation strategies and financial metrics such as return on equity and market valuation. Our findings support the thesis that environmental and innovation-oriented governance correlates with long-term profitability and market resilience. The study provides empirical evidence that ESG integration, beyond compliance, creates competitive advantage. These insights are timely for investors, policymakers, and business leaders navigating the transition to low-carbon, innovation-led economies, particularly in countries with comparable market characteristics and ESG development stages.