In light of increased consumer demand for green products and higher levels of environmental awareness in Vietnam, this research investigates the potential of green gamification to promote green eWOM. Despite increasing recognition of the role played by gamification in sustainability, the specific use of this factor to promote green eWOM, particularly in emerging markets such as Vietnam, remains underexplored. This study uses self-determination theory (SDT) to examine the impact of green gamification on green eWOM in the Vietnamese market, particularly with respect to the mediating role played by GBE in this context. Data were collected via an online survey conducted in Ho Chi Minh City, Vietnam that received 325 valid responses, a convenience sampling approach was used and the data were analysed via PLS-SEM. The results verified that green gamification significantly and positively influences GBE, which in turn, positively drives green eWOM. GBE was identified as a crucial mediator of these relationships. This research highlights actionable managerial implications that can help marketers leverage green gamification effectively. By designing games that can address consumers’ psychological needs for autonomy, competence, and relatedness, businesses can promote GBE, thus increasing positive green eWOM and promoting sustainable consumption patterns in Vietnam.