International academic mobility has surfaced as a new factor in the mechanism of cumulative advantages in early academic careers, yet its interplay with the role of doctoral mentors remains understudied compared to other factors. This research delves into the entanglement of international mobility and the doctoral mentor’s role through a 4-year longitudinal study encompassing ten postdocs from a prestigious Chinese university’s department. By employing narrative analysis across diverse cases, we found doctoral mentors wield multifaceted impacts on the access, decisions, experiences, trajectories, and outcomes of a postdoctoral international mobility through their role as teachers, sponsors, and collaborators. PhD graduates, supervised by eminent mentors with extensive overseas experiences, can enjoy a significant advantage in managing precarity and domestic social capital through mentors’ impacts on international mobility. This study offers insights into the mechanisms underlying cumulative advantages fostered through international mobility, while revealing the enduring impact of doctoral mentors throughout the academic career development.