IntroductionAcademic procrastination is a persistent challenge in doctoral education, yet the role of supervisor support remains unclear. This study examined the associations among supervisor support, impostor syndrome, neuroticism, and academic procrastination among Chinese doctoral students.MethodsAn explanatory sequential mixed-methods design was adopted. Survey data were collected from 962 doctoral students and analysed using partial least squares structural equation modelling (PLS-SEM), followed by interviews with 57 participants to further explain the quantitative findings.ResultsSupervisor support was not directly associated with academic procrastination but showed a significant, modest indirect association through impostor syndrome (β = −0.063, p < 0.05). Impostor syndrome and neuroticism were both positively associated with procrastination, whereas neuroticism did not moderate the association between supervisor support and procrastination. Interview findings indicated that self-doubt, perfectionism, and overthinking could sustain procrastination even in supportive supervisory contexts, while recognition and clear feedback helped students interpret support more constructively.DiscussionThe findings refine social support theory in doctoral education by suggesting that supervisor support is linked to procrastination primarily through students’ competence-related self-evaluations rather than through a direct behavioural pathway. In practice, supervisory support should be combined with interventions targeting impostor feelings and self-regulation.