<p>This study examines the impact of activist board representation on corporate performance in Japan, the world’s second-largest activist market amid governance system transitions. Activist board representation refers to board seats held by directors whose primary mandate is to serve the interests and strategic objectives of activist investors, often signaling increased pressure on management to implement shareholder-driven changes. Recent trends indicate that hedge funds are increasingly pursuing board representation, reflecting a broader move toward long-term involvement with target firms. In Japan, this trend aligns with governance reforms introduced through the Stewardship Code and the Corporate Governance Code since the mid-2010s, which emphasize institutional investors’ responsibility to enhance corporate value and drive sustainable growth through active engagement. Consequently, the number of activist board members in Japan has risen. Employing a difference-in-differences approach and the Speeda database, this study examines eight cases to compare performance changes between target and control firms. The findings reveal that listed target firms experience improvements in return on equity and return on assets following activist intervention, suggesting a positive influence of activist board representation. However, this effect is not observed in target firms that were delisted post-intervention. This study contributes to the understanding of activist board representation in Japan, highlighting its potential to improve the operating performance of target firms. Nonetheless, the success of such interventions is not always assured, as evidenced by cases of post-intervention delisting.</p>