["Corporate Social Responsibility and Environmental Management, EarlyView. ", "\nABSTRACT\nThis study examines the effect of green intellectual capital on firm value, with sustainability performance serving as a mediating mechanism. Drawing on signalling theory, the study explains how sustainability performance functions as a credible signal that translates internally embedded green capabilities into market value in an emerging economy context. Using panel data from 332 firm‐year observations listed on the Indonesia Stock Exchange (IDX) over the 2021–2024 period, the study employs Hayes' PROCESS Model 4 to test mediation effects. Green intellectual capital and sustainability performance are measured through systematic content analysis of sustainability reports, while firm value is proxied by Tobin's Q. The results show that green intellectual capital has a significant positive effect on sustainability performance and indirectly enhances firm value through sustainability performance. The mediation analysis reveals a complementary mediation effect, indicating that green intellectual capital influences firm value both directly and indirectly via improved sustainability performance. The study is limited to the Basic Materials sector in Indonesia and a relatively short observation period. Future research may extend the analysis to other industries, longer time horizons and additional sustainability‐related mechanisms. This study extends signalling theory by empirically demonstrating the mediating role of sustainability performance in the relationship between green intellectual capital and firm value. It provides novel evidence from an emerging market under a mandatory sustainability reporting regime, emphasising green intellectual capital as a key intangible driver of sustainable value creation.\n"]