Introduction Suicide remains a leading cause of mortality among young people aged 15-24 despite increasing investment in suicide prevention strategies across the world. System dynamics modelling (SDM) offers the potential for a more nuanced approach to suicide prevention by recognising and mapping the dynamic interactions between variables that drive population mental health and suicide outcomes; and subsequently simulate interventions to inform with what intensity and for how long investments are required to sustain the effects of any given intervention. SDM is guided by a participatory approach to model building, evaluation, and implementation. This study will present findings from the evaluation of a participatory system modelling process adopted for developing a system dynamics model to inform which suicide prevention interventions could generate the most significant reductions in rates of suicide and attempted suicide among young people aged 12-25 in North-West Melbourne, Australia. Methods Three participatory workshops were conducted with a diverse group of 10-15 stakeholders including: young people with lived experience of self-harm; carers; healthcare professionals; policymakers. Data collection was informed by a multi-scale evaluation framework evaluating the feasibility, value and impact of participatory system dynamics modelling methods, including survey questionnaires; observations through field notes; workshop recordings; semi-structured interviews. Data was analysed using codebook and reflexive thematic analysis. Results Three superordinate themes were identified: 1) Ways to facilitate effective stakeholder working (e.g. diversity and cultural representation); 2) Benefits of stakeholder engagement (e.g. the role of lived experience); 3) Changes to model following stakeholder feedback (e.g. identification of policies for testing). We will demonstrate how the participatory system dynamics modelling informed the development of a computer simulation model of mental health service pathways and suicidal behaviour among young people in North-West Melbourne. The model has been calibrated and validated using national, state, and local datasets. Conclusion This study will highlight the merit of embedding a participatory modelling approach to model development and identify future directions to maximise the potential of systems modelling and simulation in suicide prevention.