Cognitive processes are conceptualized as critical etiological factors in emotional disorders, and the transdiagnostic perspective highlights the value of investigating common cognitive risk mechanisms. We developed the Transdiagnostic Processes of Emotional Symptoms Scale (TPESS), a self-report questionnaire designed to assess a transdiagnostic cognitive risk factor. Across two studies, the TPESS was constructed and validated based on two Singaporean college student samples and a community sample from the United States (total N = 1,937). The TPESS exhibited measurement invariance across national samples, gender, and time. Evidence for reliability and validity for the TPESS was generally excellent, though discriminant validity in relation to closely aligned constructs was weaker in the U.S. sample. TPESS demonstrated incremental and unique predictive validity of various emotional symptoms and diagnoses, even after accounting for other risk factors (e.g., personality traits, emotion dysregulation). Taken together, TPESS is a promising instrument for assessing a transdiagnostic cognitive risk of emotional distress.