This research analyzes the impact of Good Corporate Governance (GCG) on firm valuation, focusing on whether stock return and financial performance moderate that relationship in IDX30 companies during 2022–2024. GCG is indicated by institutional ownership, while firm value, stock return, and financial performance are measured through PBV, total annual return, and ROA, respectively. The study employs panel data regression combined with Moderated Regression Analysis (MRA) using a Random Effects Model. Findings reveal no statistically significant influence from institutional ownership, ROA, or stock return on firm value. The results highlight that strengthening GCG implementation quality is more crucial than depending solely on ownership structure.