Committed action, a process of acceptance and commitment therapy's psychological flexibility model, is considered an understudied construct that currently can only be measured by one instrument, the Committed Action Questionnaire (CAQ‐8). This study aims at analysing the psychometric properties of the CAQ‐8 in healthy individuals and breast cancer patients. This study also aims to explore the specific meditational role of committed action in the well‐established relationship between experiential avoidance and depression symptoms. The healthy sample comprised 294 adults from the general population, and the breast cancer samples comprised 82 participants. Both groups completed the validated self‐report measures. CAQ‐8's robustness was examined through validity analyses, confirmatory factor analyses, and multigroup analysis. The meditational model was conducted using structural equation modelling. The CAQ‐8 presented good internal consistency and construct, convergent, concurrent, and divergent validity in both samples. Further, the CAQ‐8 showed incremental validity over a measure of engaged living. Findings also demonstrated measurement invariance between healthy individuals and breast cancer patients. Regarding the conducted meditational model that was also invariant between the two analysed groups, it was demonstrated that part of the effect that experiential avoidance holds on depressive symptomatology is explained by committed action. This study suggests that the CAQ‐8 is adequate for use in healthy and cancer populations. Moreover, it provides novel, empirical support regarding the links between committed action, experiential avoidance, and depressed mood, being also the first investigation to particularly study committed action in a cancer population. Implications for theory and practice are discussed.