<p>Strengthening the role of leading enterprises in the industrial chain is crucial for advancing strategic industrial transformation in emerging economies. This study constructs an indicator of leading enterprise influence based on industrial chain segmentation and develops an evaluation system for the modernization of industrial chain from six dimensions: innovation, value creation, sustainability, stability, coordination, and digitalization. Using panel data from 30 Chinese provinces covering the period 2011–2023, we empirically examine the impact of leading enterprises on the modernization of industrial chain from the perspective of agglomeration externality. The results show that leading enterprises significantly promote the modernization of industrial chain, and this conclusion remains robust after accounting for sample coverage, replacing core variables, and addressing endogeneity through instrumental variable approaches. Mechanism analysis reveals that leading enterprises exert positive effects on the modernization of industrial chain by strengthening knowledge spillovers, expanding the labor pool, and facilitating input sharing. Heterogeneity analysis further indicates that downstream leading enterprises have a stronger positive effect, and such effects are more pronounced in regions with weaker digital infrastructure, in eastern and central provinces, and in knowledge-intensive industries. This study emphasizes the importance of amplifying the multiplier effects of agglomeration externality to accelerate the modernization of industrial chain, providing new empirical evidence and policy insights for leveraging the guiding and transformative role of leading enterprises under the new development paradigm.</p>