Theory of Planned Behaviour (TPB) is employed as a conceptual foundation for the current research on environmentally responsible tourist behaviours (ERTB) in an Asian context. Extension of the TPB model has been suggested, given the limited capacity of attitude, subjective norms, and behavioural control to predict ERTB. Destination brand engagement (DBE) is conceptualised to represent the comprehensive connection between (potential) tourists and a destination built beyond travel encounters by drawing on the concept of brand engagement. The construct of DBE is incorporated to establish the extended TPB model, which can assist with a better understanding of ERTB formation. Both ERTB intention and self-reported actual ERTB are considered as the expected consequences. The hypothesised TPB-DBE model has been estimated by adopting the partial least square structural equation modelling (PLS-SEM) approach to analyse the data collected at two destinations in Malaysia and Pakistan. The literature-informed positive effects of attitude, norms, and behavioural control on ERTB are confirmed. ERTB intention is verified as an immediate predictor of self-reported ERTB, although sores for ERTB are lower than scores for intention. DBE contributes to ERTB intention and self-reported actual ERTB. The transformation from ERTB intention to on-site ERTB can be strengthened by increased DBE.