India’s GST 2.0 (rolled out in 2025) simplified tax slabs and revised exemptions, altering the economic calculus for entrepreneurs and consumers. This paper integrates GST 2.0 as a contextual policy shock into an extended Theory of Planned Behavior (TPB) framework to explain green entrepreneurial intention (GEI) and formalization intention (FI) among 328 Indian university students. The model tests Sustainability Orientation (SO) as a mediator of AT, SN, and PBC on GEI, Social Media Influence (SMI) as a moderator that amplifies social norms and sustainability framing, and GST 2.0 as a policy moderator that changes perceived compliance costs and thereby strengthens the PBC → SO → GEI/FI pathway. Using an SEM analysis combined with a randomized vignette (pre/post GST 2.0) the study finds (expected): GST 2.0 increases PBC and formalization intent for green ventures; SO mediates TPB effects; SMI magnifies norm effects; GST 2.0’s impact is strongest for respondents who report higher business-oriented social media exposure. Findings inform tax policy, entrepreneurship education, and incubation strategies to accelerate green, formal entrepreneurship in India.