Several studies have reported a negative association between obesity and academic achievement in school-aged children. In the Pacific region, the prevalence of adolescent overweight is high, but no study has considered issues of academic achievement in this population. To rectify this, we examined relationships between academic achievement and weight status in a multi-ethnic (European and Kanak) sample of New Caledonian adolescents. Objective anthropometric measures (height, weight, waist circumference) were obtained from European and Kanak New Caledonian adolescents (N = 526) between July 2018 and April 2019. Body mass index (BMI) and waist-to-height ratios (WHtR) were used as proxies of weight status. Ethnicity was self-reported and additional sociodemographic data (socioeconomic status, gender identity, urbanicity of residence, school remoteness) were extracted from relevant databases. Academic achievement scores were obtained from ninth grade national test in language, mathematics, history-geography, and sciences. Bivariate correlations showed that the associations between anthropometric indicators of weight status and academic achievement were significant in adolescents of European, but not Kanak, origin. Underweight and normal-weight European adolescents had significantly higher academic achievement than Kanak adolescents at the same weight categories. Additionally, BMI-z was significantly associated with academic achievement after controlling for socio-demographic variables, but only in adolescents of European origin. Weight status appears to be associated with academic achievement in New Caledonia, but only in adolescents of European origin. Ethno-cultural understandings and experiences may shape the ways in which weight status affects academic achievement in this context.