This study explores if, how and through what channels millennials' sustainability values translate into action when it comes to fashion garments. By testing a research model on 448 European millennials, it contrasts extant theories of planned behaviour, finding that purchase intent is often guided by unintentional, non-linear processes wherein trust in intermediaries such as celebrity influencers, rather than the fashion retailers’ corporate social responsibility (CSR) approach condition behaviour. For fashion retailers, it suggests the strategic use of influencers to (un)consciously market sustainable garments. Its novelty is built on sustainably sustaining fashion consumption in a post-pandemic world, characterised by increased online sales.