Since the outbreak of the pandemic, a large number of university students have been required to adapt to e-learning. E-learning engagement, a key indicator of academic success, is thus a great concern of educational partitioners and researchers. Although previous studies have identified various determinants of e-learning engagement, there is a paucity of research that examines the associations between university students' personalities and their engagement in e-learning. Moreover, the mechanisms underlying the personality-engagement relationship are still poorly understood. The present study used the five-factor model of personality as the main theoretical framework to explore how students with different personality traits engaged in e-learning. Additionally, it examined whether achievement emotions and adaptability mediated the personality-engagement relationship in the e-learning context. A sample of 1004 students enrolled at Guizhou University participated in an online survey to collect data for the study. Employing structural equation modeling, the findings unveiled several significant results: (1) extroversion, agreeableness, openness to new experiences, and conscientiousness exhibited positive associations with e-learning engagement, (2) neuroticism demonstrated a negative relationship with e-learning engagement, (3) the mediating effect of enjoyment as an achievement emotion was observed between personality traits (excluding neuroticism) and e-learning engagement, (4) adaptability played a mediating role in the relationship between personality traits (excluding conscientiousness and neuroticism) and e-learning engagement, and (5) the negative achievement emotion of anxiety did not operate as a mediator between personality traits and e-learning engagement. This study enriches the understanding of the relationship between personality and engagement in the emerging field of e-learning. Moreover, it offers a fresh perspective on how to investigate mechanisms underlying the relationship between personality and engagement in the e-learning context. The findings could provide a basis for instructors who wish to deploy emotional and adaptability interventions to increase university students' engagement in e-learning.