PurposeThis study aims to examine how public accounting firms can use developmental mentoring to increase knowledge sharing (KS) among employees directly and indirectly through affective organizational commitment.Design/methodology/approachThis study uses a survey of public accounting professionals to elicit participants’ demographics and their perceptions of KS, mentoring relationships and organizational commitment in their workplace.FindingsThe findings support that two categories of challenges found in developmental mentoring, demonstrating dedication and resilience and career goal and risk orientation, are directly associated with increased KS and they, along with a third, measuring up to mentor’s standards, indirectly influence KS through their positive effect on organizational commitment. Applying social exchange theory, these challenges contribute to a reciprocal relationship between the protégé and mentor, which builds the relationship between the protégé and organization.Practical implicationsThis study provides information about developmental mentoring that human resource professionals and managers in public accounting firms can use to address two persistent challenges facing them: increasing employees’ organizational commitment and encouraging employees to share their knowledge with others at work.Originality/valueThis study examines the concept of developmental mentoring, adopting three categories of mentoring challenges and applying them in the context of public accounting to examine their effect on KS.