Positive identity is essential to adolescents’ well-being and a successful transition to adulthood. Understanding factors that contribute to identity formation is important to promote healthy development. The present study applies the Positive Youth Development (PYD) framework to explore associations between adult social support and positive identity among Norwegian high school students (N = 220, Mage = 17.30, SD = 1.12). Reflecting on the ecology of adolescence, the study examined the extent to which family, other significant adults, and school support relate to different dimensions of positive identity (personal power, self-esteem, sense of purpose, and positive view of future). Further, the hierarchy of importance among the support variables was investigated. Cross-sectional data on items measuring the different dimensions of social support and positive identity were analyzed. Findings from regression analyses indicated that adult support in all three ecological contexts (family, neighborhood, and school) was significantly and positively related to positive identity and at least one of its four dimensions (β = 0.15–0.27, p < 0.05). Support from other significant adults emerged as the most important predictor, followed by family and then school support. While future research should also consider support accessed through social media, our findings extend PYD scholarship in the Norwegian context by highlighting the importance of key youth ecological contexts when fostering positive youth identity.