The Committed Action Questionnaire (CAQ-8) is an instrument developed to measure committed action, an adaptive psychological process. The main goal in the current study was to confirm the factorial structure of the Portuguese version of the CAQ-8 in a transdiagnostic clinical sample of participants diagnosed with an eating disorder (ED). Participants were 102 female outpatients (M  = 28.1, SD = 10.6; M  = 20.0, SD = 5.5) recruited from a clinical setting specialized in the treatment of ED. Confirmatory factor analysis (CFA) was used to confirm the CAQ-8's factorial structure. Both first- and second-order models revealed adequate goodness-of-fit indices (e.g. χ /df = 1.545, p = .06; SRMR = 0.049; RMSEA = 0.073; CFI/TLI > 0.95). A moderation model revealed that the conditional effect of weight, shape and eating concerns on experiential avoidance was significantly moderated by increased levels of committed action, F(3, 97) = 23.79, p < .001, accounting for 42% of the final variance. The present study supports the usefulness of the CAQ-8 as a measure of levels of committed action with patients diagnosed with an ED.