: This study aimed to explore the psychometric properties of BI-AAQ (Body-Image Acceptance and Action Questionnaire) and the body image psychological flexibility role as a mediator in a pervasive path towards binge eating in Brazilian samples. : This cross-sectional study was conducted in clinical (overweight or obese women currently in treatment for weight loss; = 330) and non-clinical (general population; = 682) groups of women. : BI-AAQ has one-factor structure, excellent internal consistency, ability to detect differences between groups and measurement invariance across samples. It was also negatively associated with self-compassion and positively associated with binge eating severity, drive for thinness and self-criticism. : This study provides data confirming the robust psychometric properties of BI-AAQ in qualitatively different samples. Furthermore, an additional study conducted in a clinical sample of women with overweight or obesity revealed that body image psychological inflexibility has emerged as a partial and significant mediator of the effect of self-criticism and drive for thinness on binge eating severity.