This study investigates the relationship between national institutional conditions and the sustainability orientation of new ventures, relying on data from the 2021 Global Entrepreneurship Monitor (GEM) Expert Survey for 43 countries. Grounded in social psychological theory—particularly the Theory of Planned Behaviour and value–belief–norm perspectives—this study examines how entrepreneurs’ attitudes, perceived social norms, and perceived behavioural control shape sustainability-oriented decision-making. Using expert data from the 2021 Global Entrepreneurship Monitor (GEM) across countries, the analysis tests whether cultural values, inclusivity norms, and perceived institutional support predict entrepreneurs’ intentions to integrate environmental goals intonew ventures. Results show that favourable attitudes toward sustainability, strong normative approval, and high self-efficacy significantly enhance sustainability orientation, while self-financing and low perceived control weaken it. These findings extendsocial psychological models of prosocial and moral behaviour to the entrepreneurship context and reveal that sustainable start-up activity depends on collective belief systems and perceived social legitimacy as much as on resources or policy incentives.