With adolescent self-harm and suicide on the rise, engaging parents as active participants in prevention programs is critical. Parents play a central role in supporting their child’s socio-emotional development and mental health; however, few school or community-based programs involve them as active participants. Co-design offers a structured, collaborative approach to develop interventions that are relevant, usable, and tailored to parental needs. The primary aim of this study was to co-design a digital intervention with parents to strengthen their capacity for self-harm prevention. The secondary aim was to understand parental content and format preferences, ensuring the intervention was both engaging and acceptable. The co-design process followed Hawton’s framework for the co-production and prototyping of public health interventions and was conducted in three phases. Phase One involved reviewing evidence and consulting stakeholders, including clinicians and parents, to inform the initial intervention concept. Phase Two focused on co-production, with three workshops engaging parents with lived experience (n = 6) and two for those without known lived experience (n = 8) to identify needs, priorities, and preferences. Phase Three involved presenting a website prototype, which was iteratively refined based on feedback and re-shared to guide further development. Data was analysed using deductive framework and thematic analysis. Parents from both streams wanted information that was clear, practical, and interactive, though content preferences differed. Parents with lived experience highlighted information addressing early warning signs and strategies to promote emotional safety, drawing on personal experiences. Parents without lived experience emphasised preventive strategies and tools to support general wellbeing, ensuring content was relevant for all parents. Most parents, regardless of experience, preferred web-based formats with embedded instructional videos, downloadable resources, and interactive activities to support skills practice. The co-design process also revealed priorities not previously incorporated, including a dedicated section on technology use and adaptations to enhance suitability for culturally and linguistically diverse families. These insights directly shaped the prototype’s design, navigation, and functionality, demonstrating the value of integrating diverse perspectives to uncover needs and preferences that might otherwise be overlooked. By integrating lived experience and broader community perspectives, this study identified parenting strategies that may mitigate self-harm risk and approaches to engage parents before the onset of self-harm. The intervention’s efficacy will be evaluated in a pilot trial next year, providing evidence to guide future parent-focused suicide prevention initiatives, providing a critical step to healthier, happier futures.