Purpose This study examined the impact of peer mentoring on identity transformation amongst women in prison, exploring how peer mentoring roles develop non-offender identities, contributing to the desistance process. Design/methodology/approach A qualitative, interpretative approach was adopted. The research was undertaken at a female prison in England and Wales. Data was collected through semi-structured interviews with peer mentors, mentees, project workers and prison officers, alongside focus groups. Thematic analysis was used to analyse the findings. Findings Being a peer mentor contributes positively to identity transformation for women in prison, fostering a legitimate, non-offender identity critical to the desistance process. Mentors view their role as a desistance signal through their interactions with prison staff. However, it can lead to role conflict and tension with other women in prison and prison staff. Research limitations/implications Future studies should consider longitudinal approaches to capture the long-term effects of peer mentoring upon desistance. Practical implications Recommendations include leveraging peer mentoring as a rehabilitative intervention, providing ongoing support for mentors and educating prison staff on programme benefits to foster a supportive environment. Social implications Enhancing peer mentoring programmes can improve the well-being of women in prison and support their reintegration into society. Originality/value This study examined identity transformation in female peer mentors in prison through the lens of social identity and group membership. To the author’s knowledge, no previous studies have focused centrally on identity or applied social identity theory to explore the psychological mechanisms behind these transformations.