Nutritional environment in early life is a key factor for brain development and function. It is important to understand the relationship between nutrition in early life and academic achievement in adolescence. The birth cohort of the Pacific Islands Families (PIF) study was born in the year 2000. When their child was six weeks old, mothers were asked questions concerning food security over the past year. Two binary measures of food security were derived as previously used in PIF and also by the Ministry of Health (MOH). In 2020, records of academic achievement from the National Certificate of Educational Achievement (NCEA) for 649 (317 female, 332 male) cohort members showed progressive achievement at levels 1, 2, and 3 of NCEA and allowed University Entrance (UE) to be assessed. The prevalence of food insecurity was not different for sex but high at 29% and 42% using the PIF and MOH definitions of food insecurity, respectively. More females (27%) than males (18%) achieved UE as their highest qualification, and more males (40%) than females (31%) achieved NCEA levels 1 or 2 as their highest qualification. UE was achieved by 25% of those born into food-secure households and 17% from food-insecure households. Logistic regression demonstrated that the odds of achieving UE were 1.8-fold (95% CI 1.2, 2.6, p = 0.003) higher in females than males and, independently, 1.6-fold (95% CI 1.1, 2.5 p = 0.026) higher if the household was food secure. This work emphasises the importance of maternal and early-life food security for subsequent academic achievement and the well-being of future generations.