Assessing the impact of body image on engagement in a range of life domains is important; however, there is a lack of validated measures for adolescents. The current research developed the Body Image Life Disengagement Questionnaire (BILD-Q) and validated it among four samples of British adolescents. Study 1 (N = 1707; 11-13 years) indicated a 9-item unidimensional scale based on Exploratory Factory Analysis. In Study 2 (N = 1403; 11-13 years), Confirmatory Factor Analysis (CFA) showed an acceptable fit overall, but better among girls than boys. Further exploration with CFA in Study 3 (N = 2034; 13-14 years) showed a good to excellent fit overall, and acceptable among both boys and girls. The scale showed good internal consistency and test-retest reliability, and gender invariance indicated the scale can be used comparatively. In Study 4 (N = 288; 13-14 years), convergent validity was supported via expected relationships with body image and related constructs. Concurrent and predictive incremental validity were also evidenced via explaining significant unique variance in well-being. These studies provide support for the BILD-Q as a reliable and valid measure of broader impacts of body image among adolescents, which may benefit intervention evaluation and policy change efforts.