Sustainable consumption is evolving as consumers respond to climate concerns, ethical sourcing, environmental governance, and corporate accountability. However, sustainability-driven purchase intent varies by cultural norms, environmental literacy, purchasing power, and social values. This study compares sustainable buying intent across diverse cultural regions—North America, Europe, Asia, Africa, and South America—using survey responses from 1,420 participants, interviews with sustainability researchers, and secondary data from market reports. Findings indicate that cultures high in collectivism and long-term orientation exhibit stronger intentions toward sustainable purchases, whereas high indulgence and low environmental regulation reduce adoption rates. A cultural–behavioral sustainability model is proposed to guide global green marketing strategies.