Introduction Rates of mental health difficulties among girls and young women in the UK have risen sharply, and disproportionately so for those from marginalised groups. My Story and Me is a new digital public mental health intervention that uses storytelling to reduce stigma, increase awareness and support early help-seeking among girls and young women aged 14–18. The feasibility study aims to determine the acceptability of the intervention and future full trial, including assessing optimal settings and meaningful changes in the primary outcome measure (anxiety and depression). Methods and analysis This is an 18-month mixed-methods, uncontrolled feasibility study conducted in secondary schools, further education colleges and community organisations across the UK. We will recruit 120–180 participants. Quantitative data will be collected at baseline and 7-month follow-up. The primary outcomes are anxiety and depression, and secondary outcomes are social support, mentalising, stigma, quality of life, loneliness, empowerment, intervention acceptability, resource use and randomisation acceptability. Platform-level engagement data will assess adherence and fidelity. Qualitative interviews with young women and staff will explore acceptability, feasibility, mechanisms of change and views on trial procedures, including randomisation in a future full trial. Analysis will be descriptive and exploratory, including comparisons across settings and priority groups (LGBTQIA+, neurodivergent and those experiencing digital poverty). A framework and reflexive thematic analysis approach will be used for qualitative data. Prespecified progression criteria will inform decisions about advancing to a full cluster randomised trial. Ethics and dissemination The University College London Research Ethics Committee (0692) has approved the My Story and Me protocol. Interested participants will be required to complete an expression of interest and consent form to take part in the study, and young people under 16 years old will be required to obtain parent/carer informed consent. Results will be disseminated through peer-reviewed publications, lived experience summaries, a policy briefing and academic conference presentations. Trial registration number ISRCTN12191423 .