Nursing professionalism relates to the knowledge, skills, conduct, behaviour and attitudes of registered nurses. Difficulties related to student assessment of professionalism have been anecdotally described as a disparity between the meaning of the term ‘professionalism’ to nurses and its application and measurement in clinical practice. The aim of this study was to develop a professional practice competency for undergraduate nurses on clinical placement. An exploratory sequential mixed-methods approach with a two-phase design was used to develop the competency. Phase one, the Delphi method with 16 expert nurses, was used to develop the competency. This involved the thematic analysis of key statements over four rounds, five key themes were identified (attitudes, communication, knowledge, standards, relationships) that formed the framework and 33 individual competency statements. This was followed by phase 2, content validity, using the Table of Specification with 58 clinical facilitators. The findings confirmed the statements (80% consensus) deemed important to assess the essential construct of nursing professional practice. It is envisaged that the professional practice competency will assist student insight into their professional role and subsequently allow adjustment and achievement of professional practice competency