University entry and the passage through university is a time of great change. The extent to which students are able to adjust to successfully navigate this change (adaptability) is likely to influence their academic outcomes. Prior research has identified a link between university students' adaptability and academic achievement via behavioural engagement. The current longitudinal study extends this research by examining whether university students' adaptability predicts degree completion via behavioural engagement. Undergraduate students (N = 186) were surveyed for their adaptability and behavioural engagement at degree commencement. Their completion status was extracted from the University Records System at the end of the degree. Findings showed that adaptability predicts both positive and negative behavioural engagement, and that negative (but not positive) behavioural engagement predicts degree completion. Adaptability was also found to influence degree completion indirectly via negative behavioural engagement. These findings hold important theoretical and practical implications for educators and researchers seeking to understand how students manage the transition to university and the extent to, and mechanisms by which students' adaptability is associated with university degree completion.