Children Growing Up in LiverpooL (C-GULL) is a novel longitudinal research platform combining civic (CityLab) and birth (10,000 first-borns; triad design) cohorts. The scientific and civic aims share a need to better understand: non-communicable diseases trajectories, mental health and developmental/educational prosperity by focusing on connected determinants of child health in one of the UK’s most disadvantaged cities. We will identify early-life determinants and interventions for diseases including childhood/adult obesity, cardiovascular disease, asthma and mental health, and evaluate the impacts of systems change interventions to improve early years outcomes. The findings will be relevant for tackling health inequalities globally. Women will be recruited during the first trimester of pregnancy over a 42-month period at Liverpool Women’s Hospital. Extensive biological, biometric, socio-demographic and psychosocial information will be collected at two time points in pregnancy, at birth, 2–3 months, one year, two years and five years of age. The deep clinical, psychosocial and molecular phenotyping of this large cohort will be linked to routinely-collected data on the health & social care, education and welfare systems underpinning child health, lessening the burden on participants, and allowing the collection of additional data via emerging digital media that instrument behavioural, social and environmental factors.