AbstractTo date, research has predominantly focused on identifying the antecedents of sustainable consumption, but little work has been done to understand the impact of the consumption of sustainable brands on consumer emotions and behaviours thereof and how it varies across generations. This study attempts to analyse the relationship between consumption of sustainable brands and brand happiness, and the likelihood of it resulting in brand evangelism. We used the mall intercept method to collect responses from 564 respondents. We used structural equation modelling (SEM) to verify the research model and hypotheses and Hayes Process macro to test mediation and moderation impact. The study concludes that the consumption of sustainable brands triggers a positive emotional response in the consumer by evoking a feeling of happiness, which leads them to evangelise the brand. Thus, evangelists disseminate positive word of mouth and repurchase the brand, as well as engage in oppositional brand referrals to strengthen their relationship with the brand. The study further confirms the moderating role of generation cohorts in the relationship between brand happiness and brand evangelism. Gen Z is more likely to be an evangelist for sustainable brands as compared to other cohorts. The results corroborate with the self‐perception theory, which has been used as a theoretical base. In addition, managers should prioritise sustainability as a driver of brand happiness to effectively engage consumers, especially Generation Z, while aligning marketing strategies for consumer behaviour.