Sustainable behaviour promotes pro-ecological behaviour and is a practice of consuming and utilizing resources responsibly. The ongoing COVID-19-induced pandemic has already put economic, social and psychological distress across the globe. Meanwhile, it has become vital to think of issues related to the sustainable management of resources. Behavioural norms play a prominent role while promoting sustainable living. This research examines how the sustainable dimension in one’s behaviour influences the decision-making in their daily life. Previous studies have shown the importance of sub-factors (...) like happiness, diversity constraint and frugal actions as factors affecting sustainable behaviour. These indicators mainly define the action one will choose to react to while buying and consuming different resources. The study identifies happiness as the mediating variable which influences the relationship between the predictor variables—mindfulness and diversity acceptance and the criterion variable—frugality-linked sustainable behaviour. With a sample of 324 participants, Baron and Kenny’s mediation model was outlined to test the mediation. Results showed a positive relationship between frugality, diversity, mindfulness and happiness. Happiness was found to be mediating between mindfulness, diversity acceptance and frugality-linked sustainable behaviour indicating that mindfulness and diversity acceptance alone have limited potential to impact the frugality-linked sustainable approach that individuals take. Happiness, as explained through a positive frame of mind, plays a very important role in enhancing sustainability behaviour. (shrink)