Previous research has found that, when firms engage in environmental sustainability practices, they tend to give a consistent signal to external stakeholders by acting in a more responsible, transparent, and ethical manner, and these firms tend to exhibit high earnings quality. However, other studies have found that those activities may mask a poor earnings quality. On the other hand, firms with high debt levels face constraints in raising funds. In this study, we expect these firms, when involved in environmental reporting practices, to reveal an increase in their earnings quality in order to improve their ability to capture financing. Thus, we analyze whether the level of environmental disclosure and a firm’s debt increase earnings quality. To analyze the former association, we develop an environmental sustainability reporting index (ESReporting), based on GRI standards, using the content analysis for Portuguese firms from 2016 to 2020. We use earnings persistence as a proxy for earnings quality because it is a fundamental characteristic to determine firm value. Regarding debt, we include a financial indicator to analyze its effect on earnings persistence. To test the hypotheses, we estimate a multiple linear regression, applying panel data. Our results suggest that ESReporting and debt tend to positively affect earnings persistence. In addition, our evidence suggests that ESReporting produces a higher positive impact then debt. These results show that ESReporting and debt may be used as regulating mechanisms of earnings management. Besides, this article brings some insights to the improvement of earnings quality resulting from a higher commitment to environmental disclosure and contributing to monitoring managers’ activities.