Background Life course studies are designed to “collect once, use multiple times” for observational and, increasingly, interventional research. Core Outcome Sets (COS) are minimum sets developed for clinical trials by multi-stakeholder consensus methodologies. We aimed to synthesize published COS that might guide outcomes selection for early life cohorts with an interventional focus. Methods We searched PubMed, Medline, COMET, and CROWN for COS published before January 2021 relevant to four life stages (pregnancy, newborns, children <8 years, and parents (adults aged 18–50 years)). We synthesized core outcomes into overarching constructs. Results From 46 COS we synthesized 414 core outcomes into 118 constructs. “Quality of life”, “adverse events”, “medication use”, “hospitalization”, and “mortality” were consistent across all stages. For pregnancy, common constructs included “preterm birth”, “delivery mode”, “pre-eclampsia”, “gestational weight gain”, “gestational diabetes”, and “hemorrhage”; for newborns, “birthweight”, “small for gestational age”, “neurological damage”, and “morbidity” and “infection/sepsis”; for pediatrics, “pain”, “gastrointestinal morbidity”, “growth/weight”, “breastfeeding”, “feeding problems”, “hearing”, “neurodevelopmental morbidity”, and “social development”; and for adults, “disease burden”, “mental health”, “neurological function/stroke”, and “cardiovascular health/morbidity”. Conclusion This COS synthesis generated outcome constructs that are of high value to stakeholders (participants, health providers, services), relevant to life course research, and could position cohorts for trial capabilities. Impact We synthesized existing Core Outcome Sets as a transparent methodology that could prioritize outcomes for lifecourse cohorts with an interventional focus. “Quality of life”, “adverse events”, “medication use”, “hospitalization”, and “mortality” are important outcomes across pregnancy, newborns, childhood, and early-to-mid-adulthood (the age range relevant to parents). Other common outcomes (such as “birthweight”, “cognitive function/ability”, “psychological health”) are also highly relevant to lifecourse research. This synthesis could assist new early life cohorts to pre-select outcomes that are of high value to stakeholders (participants, health providers, services), are relevant to lifecourse research, and could position them for future trials and interventional capability.