PurposeThis study explores the dynamics of companies’ green knowledge sharing (GKS) within the tourism sector, focusing on its influence on green electronic word-of-mouth (eWOM) intention via the mediation of tourists’ green engagement behaviour. Additionally, the study considers the moderating effects of green destination psychological ownership and perceived injunctive norms of green self-expression online on the pathway from green knowledge sharing to tourists’ green engagement behaviour to green eWOM.Design/methodology/approachThe primary dataset, consisting of 902 valid responses obtained through time-lagged surveys administered to environmentally conscious tourists, was analysed using structural equation modelling (SEM) by PROCESS package for R.FindingsFindings indicate that green destination psychological ownership enhances the mediation effect of tourists’ green engagement behaviour on green eWOM intention, reinforcing the sense of personal investment and belonging among tourists. Conversely, perceived injunctive norms of green self-expression online moderate this pathway by shaping the social norms and acceptability of green behaviours online.Practical implicationsTo effectively spread green knowledge, tourism businesses should focus on enhancing tourists' psychological ownership of green destinations and align their communications with the perceived norms of green expression online. This strategy not only deepens tourists' environmental commitment but also stimulates active participation in spreading sustainable practices.Originality/valueThis study contributes to the green marketing literature by revealing how intrinsic and extrinsic motivational factors interact to influence green engagement and eWOM intention in the tourism industry, aiding marketers in strategically fostering green value co-creation and enhancing sustainable practices through targeted green knowledge sharing.