<p>This study proposes the Cognitively and Morally Contingent Theory of Planned Behavior (CMC-TPB) to explain when the intention-behavior link in sustainable consumption holds. Rather than treating media literacy and moral disengagement as parallel predictors, CMC-TPB positions them as the cognitive and moral preconditions under which TPB-based intention formation remains credible. Green purchase intention is then more likely to translate into buying behavior when enactment is supported by efficacy beliefs and cohort-linked consumption conditions. We test CMC-TPB using survey data from 317 Vietnamese consumers in a media-saturated, collectivist emerging market where responsibility for sustainable consumption is often diffused across individuals, families, firms, and regulatory actors. The data were analyzed using PLS-SEM with mediation, moderation, and multi-group comparisons across Generation Z and Generation Y. Results show that media literacy significantly reduces moral disengagement and strengthens green purchase intention, while moral disengagement undermines intention formation. Green purchase intention strongly predicts green buying behavior, and indirect effects support the proposed cognitive-moral pathways. Boundary analyses further show that perceived consumer effectiveness strengthens intention enactment, while generational differences emerge primarily in intention-behavior consistency: this link is stronger among Generation Y than Generation Z, although the moderating effect of perceived consumer effectiveness does not differ significantly across cohorts within the shared collectivist context. The study advances TPB-based ethics and sustainability research by specifying the cognitive-moral contingencies under which intention becomes action and clarifies when and for whom TPB works in sustainable consumption. It also offers actionable implications for anti-greenwashing communication and targeted media-literacy interventions.</p>