Research about autistic people’s subjective experiences with music and its impact on their wellbeing is limited, despite its common presence in public spaces and support services. To provide an empirical framework and tools for future research, we examined the relevance of the participatory music engagement for mental well-being model for autistic adults. The model outlines four pathways through which music supports well-being: managing and expressing emotion, providing respite, facilitating self-development, and facilitating connections. Based on the model, we developed a new questionnaire, the Participatory Music Engagement for Mental Well-being (PaMEW), and collected responses from 63 autistic adults. We found that most respondents believed the items were relevant to their experiences of the relationship between music and well-being, that the factorial structure of their responses aligned with the model, and that their comments reflected the four pathways; however, they also highlighted nuances not addressed by the model. The study underscores the need for nuanced tools that reflect the unique ways autistic individuals use music to support their well-being, suggesting future revisions of PaMEW in collaboration with the autistic community to enhance its relevance and clarity.