Abstract Background Peer assessment can support the development of professionalism by providing feedback that enables learners to reflect on their professional behavioural attributes. Approach We developed and implemented an innovative online peer assessment and feedback tool. Students were encouraged to nominate 12 peer assessors to anonymously conduct their assessment. Assessors were presented with a list of 32 adjectives that described professional behavioural attributes within four domains (integrity, conscientiousness, agreeableness and resilience) and asked to rate the student by selecting a minimum of two adjectives in each domain and to provide free‐text comments. The feedback was presented as a collated word cloud and free‐text comments. All students had the opportunity to discuss their profiles with a staff member. Evaluation Our mixed‐methods evaluation found that all students participated, and they valued the peer assessment and feedback process. Although the assessment was formative and confidential, students were reluctant to provide negative comments about their peers. ‘Disengaged’, ‘aloof’ and ‘argumentative’ were the most likely negative adjectives that indicated students with low‐level professionalism concerns. Implications Future development will focus on introducing students who can act as peer champions for the process and repeating the peer assessment over time to identify the change in professionalism development.