With the increasing awareness of sustainable development, the ESG performance has become a focal point for both companies and their stakeholders. This study, Chinese A-share listed companies as an example, constructs a sample of paired enterprises and customers to examine the impact of customer ESG performance on corporate carbon productivity and its underlying mechanisms. The research demonstrates a positive relationship between customer ESG performance and corporate carbon productivity, indicating the presence of a supply chain contagion effect. In terms of influencing mechanisms, customer ESG performance primarily enhances corporate carbon productivity by increasing pollution control investments and improving gross domestic product. Further investigation reveals that the improvement in customer ESG performance has a more significant impact on corporate carbon productivity when the company is larger in scale, operates in less-polluting industries, and engages in export activities. This study enriches the relevant research on corporate carbon productivity from an external partner perspective and provides valuable insights for supply chain enterprises on how to enhance carbon productivity and sustainable competitive advantage.