To determine whether a formal mentoring programme assists nurse practitioner candidates to develop competence in the clinical leadership competencies required in their advanced practice roles.Nurse practitioner candidates are required to show evidence of defined clinical leadership competencies when they apply for endorsement within the Australian health care system. Aiming to assist the candidates with the development or enhancement of these leadership skills, 18 nurse practitioner candidates participated in a mentoring programme that matched them with senior nurse mentors.A pre-postlongitudinal intervention study.Eighteen nurse practitioner candidates and 17 senior nurses participated in a voluntary mentoring programme that incorporated coaching and action learning over 18 months in 2012 and 2013. Participants completed a pen and paper questionnaire to document baseline measures of self-reported leadership practices prior to commencement of the programme and again at the end of the programme.The mentors and the nurse practitioner candidates qualitatively evaluated the programme as successful and quantitative data illustrated significant improvement in self-reported leadership practices among the nurse practitioner candidates. In particular, the nurse practitioner candidates reported greater competence in the transformational aspects of leadership, which is directly related to the nurse practitioner candidate clinical leadership standard.A formal, structured mentoring programme based on principles of action learning was successful in assisting Australian advanced practice nurses enhance their clinical leadership skills in preparation for formal endorsement as a nurse practitioner and for success in their advanced practice role.Mentoring can assist nurses to transition to new roles and develop knowledge and skills in clinical leadership essential for advanced practice roles. Nurse managers should make greater use of mentoring programmes to support nurses in their transition to new roles.