Childhood obesity remains a major public health issue globally. Understanding how early-life dietary, lifestyle, socioeconomic, and environmental factors shape obesity risk is critical for designing targeted prevention strategies. This study aimed to identify distinct early-life cluster patterns among Australian children and examine their associations with longitudinal obesity outcomes from ages 4–15 years. Data came from the Longitudinal Study of Australian Children (LSAC) Birth cohort (N = 5107). An analytic sample of 4246 children with complete data at Wave 2 (aged 2–3) was analysed. Latent Class Analysis (LCA) was applied to identify early-life clusters, and body mass index (BMI) categories, underweight, normal weight, overweight, and obesity, were tracked across Waves 3–8 (ages 4–15). Chi-square tests and multinomial logistic regression (adjusted for maternal employment, neighbourhood safety, child screen time) examined associations between clusters and obesity outcomes. Four clusters were identified: (1) Risky Diet & Socioeconomically Disadvantaged, (2) Healthy Diet & Urban Affluent, (3) Mixed Diet & Moderate SEP Large Families, and (4) Healthy & Wealthy Metro Families. Children in Cluster 1 had persistently higher obesity prevalence (rising from 9% at age 4–5 to 17% at age 14–15), whereas Cluster 4 maintained the lowest (2–4%). Adjusted models showed significantly higher odds of obesity in Cluster 1 across all waves (AOR 2.4–7.5; p < 0.01). Distinct socio-dietary clusters established in early childhood predict divergent obesity outcomes up to age 15. Interventions addressing early nutrition, socioeconomic disadvantage, and environmental inequities are crucial to mitigate long-term obesity risk.