Communicating a persuasive rationale that explains the client’s problems and how psychotherapy can relieve them, has been proposed as a crucial determinant of outcomes that combats the client’s state of distress, promotes positive expectations, and facilitates the working alliance. However, it remains 1 of the least investigated psychotherapist’s facilitative interpersonal skills without a validated measure. The present correlational observational study aimed to develop a rating scale that measures the psychotherapist’s persuasiveness, and to examine its relationship with the working alliance. Based on a literature review of the psychotherapist’s persuasiveness, the Therapist’s Persuasiveness Rating Scale (TPRS) was constructed. Seventeen psychotherapy session recordings were used to validate the scale through exploratory and confirmatory factor analysis, validity, reliability, and sensitivity assessment. Fourteen psychotherapy session recordings with clients suffering from anxiety were rated using the TPRS and the Working Alliance Inventory-Observer Version-Short Form (WAI-O-S) to examine the relationship between the 2 variables. The validation process resulted in a 4-factor 10 items scale. Except for the discriminant validity, which was revealed to be inadequate, the TPRS showed to be a valid, reliable, and sensitive measure of the psychotherapist’s persuasiveness. Despite a nonsignificant correlation found in Spearman’s correlation, a linear regression model suggested that the psychotherapist’s persuasiveness explains 65.1% of the working alliance at the beginning of the session. The TPRS revealed a promising measure with good psychometric qualities to advance the research on the psychotherapist’s persuasiveness. There is some suggestion of the psychotherapist’s persuasiveness effect on the working alliance, but the result missed statistical significance.