The transition from university to the labour market is a critical phase in graduate professional development, requiring the ongoing formation of a clear professional identity. Drawing on the graduate identity approach and mentoring theory, we argue that internship, as a key form of work-integrated learning (WIL) experience, represents a liminal space across academic training and workplace practice systems. Practitioners serving as internship mentors serve as bridges, fostering the process of anticipatory socialisation, thereby supporting graduates to meaningfully shape their envisioned professional identity and feel worthy of being employable. This three-wave longitudinal study explores whether and how mentoring contributes to graduates’ emerging professional identity and perceived employability through graduate anticipatory socialisation. It was conducted with 142 Italian Psychology graduates at mid-internship, end-of-internship, and 6–18 months post-internship. Structural Equation Modelling (SEM) results supported the hypothesised model and the full mediation of anticipatory socialisation on both outcomes. These findings position mentoring as a critical enabler of identity work in liminal spaces between academic study and employment, fostering graduates’ readiness for the labour market. The study also highlights the importance, for educational institutions and policymakers, of embedding structured mentoring into WIL programmes to support intentional identity development and sustainable career trajectories.