Background This study focused on exploring the longer-term participation needs of children and young people with acquired brain injury (CYP-ABI) and their families in one region of the UK and identifying the barriers and facilitators of their participation and well-being to inform the development of a behavioural change intervention for clinical implementation. Methods Qualitative interviews were conducted with CYP-ABI and parents. Focus groups were created with health, education, care and charity stakeholders. The International Classification of Functioning, Disability and Health (ICF) and the Behaviour Change Wheel (BCW) were used to map needs, barriers and facilitators. Results A total of 10 CYP/parent dyads (n = 20) and 17 health, education, care and charity stakeholders were included in this study. Unmet participation needs were mapped to the ICF and barriers/facilitators to the BCW. Significant unmet needs impacting CYP-ABI participation and family well-being were found. Barriers spanned 'Capability', 'Opportunity' and 'Motivation', the greatest being knowledge, skills, social influences, environmental context and resources, social identity and emotion. Facilitators included increasing awareness and understanding, supporting parents, long-term access to specialist assessment and rehabilitation, peer support and integrated collaborative pathways. Conclusion The long-term impact of ABI on CYP and families' participation and well-being were significant, with barriers spanning every sector and level of society. Implementation of collaborative, cross-sector (education, health and social care) accessible and family-centred care pathways is needed to meet the long-term needs of CYP-ABI and their families, ensuring equity of access. Multi-modal, family-centred, needs-led, theory-based interventions should be co-developed with CYP, families and stakeholders to improve the health and well-being outcomes and the lives of CYP-ABI and their families.