INTRODUCTION: Children and young people (CYP) in the UK have poor health outcomes, and there is increasing emergency department and hospital outpatient use. To address these problems in Lambeth and Southwark (two boroughs of London, UK), the local Clinical Commissioning Groups, Local Authorities and Healthcare Providers formed The Children and Young People's Health Partnership (CYPHP), a clinical-academic programme for improving child health. The Partnership has developed the CYPHP Evelina London model, an integrated healthcare model that aims to deliver effective, coordinated care in primary and community settings and promote better self-management to over approximately 90 000 CYP in Lambeth and Southwark. This protocol is for the process evaluation of this model of care. METHODS AND ANALYSIS: Alongside an impact evaluation, an in-depth, mixed-methods process evaluation will be used to understand the barriers and facilitators to implementing the model of care. The data collected mapped onto a logic model of how CYPHP is expected to improve child health outcomes. Data collection and analysis include qualitative interviews and focus groups with stakeholders, a policy review and a quantitative analysis of routine clinical and administrative data and questionnaire data. Information relating to the context of the trial that may affect implementation and/or outcomes of the CYPHP model of care will be documented. ETHICS AND DISSEMINATION: The study has been reviewed by NHS REC Cornwall & Plymouth (17/SW/0275). The findings of this process evaluation will guide the scaling up and implementation of the CYPHP Evelina London Model of Care across the UK. Findings will be disseminated through publications and conferences, and implementation manuals and guidance for others working to improve child health through strengthening health systems. TRIAL REGISTRATION NUMBER: NCT03461848.