Students’ experiences and practices regarding English as a lingua franca (ELF) have been central to the discussion in research on intercultural communication in academia as it provides the basis for English language policy and practices in the international university. To date, however, few previous studies have explored diverse factors for perceptions of ELF communication with a single framework. To fill this gap, this study provides the integrative research model for perceptions and behaviours regarding ELF communication in the international university context, using Theory of Planned Behaviour. It further explores the effect of those factors on actual intentions to engage in ELF communication. Data were collected from 232 questionnaires and seven interviews on the offshore campus of a Hong Kong university in mainland China. Findings showed that factors such as acceptance, social expectations, the sense of control over linguistic knowledge for intercultural communication, and self-esteem had significant effects on intentions. The study concluded that ELF speakers’ decision-making process to engage in ELF communication is not simply based on individual behaviour, but on social performance in academic communities of practice. This study suggests academic and educational implications for incorporating the ELF perspective into English language policy and practices in the international university. © 2020 Walter de Gruyter GmbH.