Climate change and environmental degradation are among the most important challenges of the 21st century. Some human behaviours have played a key negative role in the sustainability of the planet. Therefore, studying the psychological mechanisms that may increase environmental responsible behaviour (ERB) is a key issue. Research has consistently shown that gratitude, a "wider life orientation towards noticing and appreciating the positive in the world", is a strong predictor of several pro-social behaviours in general life settings. More recently, a few studies suggest that gratitude at work could also be a predictor of employee's pro-social behaviours, such as ERB. Indeed, ERB is considered a particular case of broader helping/pro-social actions. Further, drawing on gratitude research, environmental psychology and positive organizational scholarship (POS), we theorized that gratitude at work will prospectively predicts higher employee's ERB. Further, we conducted a three-waves longitudinal study (N = 1477), with six months between each wave among a representative sample of workers in Chile. We tested a Cross-lagged Panel Model. In support of our hypothesis, we found that gratitude at work at T1 (T2) prospectively predicts higher employee's ERB at T2 (T3). Unexpectedly, we also found a reverse link: Employee's ERB at T1 (T2) prospectively predicts higher gratitude at work at T2 (T3). The reciprocal link already found not only extend gratitude research in the workplace. It also gives promising insights about understudied psychological mechanisms that may help to protect the future of the Earth. Key implications for gratitude, environmental psychology and POS are discussed.