Grounded in the person–environment fit theory and an identity-based perspective, this study investigated the relationship between perceived overqualification and knowledge hiding, focusing on the mediating role of future work self-salience and the moderating role of the growth mindset. We suggest that perceived overqualification as a person–job misfit would negatively impact employees’ salient hoped-for work identities, representing a low level of future work self-salience. The diminished salience of a future work self leads employees to hide their knowledge. Furthermore, the growth mindset exacerbates the negative impact of perceived overqualification. We conducted a three-wave survey with 482 employees from knowledge-intensive industries. The results revealed that perceived overqualification boosted knowledge hiding by decreasing employees’ future work self-salience. The growth mindset enhanced the negative relationship between perceived overqualification and future work self-salience. Thus, the indirect effect of perceived overqualification on knowledge hiding via future work self-salience was more significant for those with a stronger growth mindset. Our findings contribute to the literature on person–job fit and knowledge behavior while providing practical insights for managing and guiding talented employees in knowledge management.