This study aimed to assess the connection between HEXACO personality traits (i.e. honesty–humility, emotionality, extraversion, agreeableness, conscientiousness, and openness to experience) and knowledge sharing behaviour (KSB) of university academic staff. Moreover, based on the theory of planned behaviour (TPB), this study aimed to examine the underlying process through which HEXACO personality traits contribute to academics’ KSB by examining mediating role of affective commitment. With a structured questionnaire survey, the data was conveniently collected from 234 full-time university faculty members employed in 20 private universities located in Bangladesh. Structural equation modelling partial least square (SEM-PLS) was utilised to analyse the research model. The results revealed that, with the exception of emotionality, all HEXACO personality traits (i.e. honesty–humility, extraversion, agreeableness, conscientiousness, and openness to experience) have positive direct effects on academics’ KSB. The study further showed that the effects of honesty–humility, extraversion, agreeableness and conscientiousness on KSB were significantly mediated by affective commitment. Thus, universities should focus on academics’ personality profiles to improve knowledge sharing practices within the institutions. In particular, personality test should be introduced in the selection process of university teachers to identify the candidates with desirable personality traits. The findings offer a new understanding of how HEXACO personality traits result in academics’ KSB directly as well as via affective commitment.