From 2015, China began to promote eco-sustainability in the Belt and Road Initiative (BRI) through not only vision statements but also specific guidelines and governance initiatives. What has driven these policy changes? Bringing together theories of norm localization, norm subsidiarity, and policy deliberation, we argue that China’s move toward green BRI began as a norm localization process where environmental norms emerged in the open policy space created by China’s top leaders carrying the ambition to make the BRI a new global governance model. After adopting a broad norm on environmental stewardship, state bureaucracies found opportunities to create procedural and operational rules. A novel procedural rule-making methodology emphasizing inclusive dialogue with host countries has emerged, driven by top leaders’ pursuit of international leadership and preexisting local norms guiding South–South cooperation. With operational rules, different actors follow their preferences to localize existing international standards or develop new ones.