<p>Against the global backdrop of leveraging digitalization for sustainability transitions, this study explores how state-led e-commerce policies shape trade sector green productivity (GP) in emerging economies. Taking China’s National E-commerce Demonstration Cities (NEDC) initiative as a quasi-natural experiment, we employ a staggered difference-in-differences (DID) model and panel data from 291 prefecture-level cities (2005–2023) to decipher the policy’s efficacy mechanisms. Results reveal that the NEDC policy significantly enhances trade sector GP through three complementary channels: green technology innovation, green financial resource allocation, and green industrial agglomeration. Environmental regulation positively moderates this effect, amplifying the digital-green synergistic dividend. Heterogeneity analysis confirms more pronounced policy impacts in eastern regions, economically developed cities, and areas with advanced transportation and digital infrastructure—with the “digital dividend multiplier effect” most prominent in the information development dimension. Theoretically, we extend the Porter Hypothesis by constructing a “Digital-Environmental Co-evolution” framework, illustrating how institutional innovation mediates the interaction between digitalization and green development. Practically, we propose a tiered, context-adaptive policy toolkit for emerging economies, prioritizing infrastructure-augmented regulatory bundling in early digitalization phases. These findings provide actionable insights for global digital-green transition practices, facilitating the cross-border adaptation and promotion of policies integrating digitalization and green development.</p> Graphical Abstract <p></p>