ABSTRACTBackgroundInterpersonal synchrony entails the coordination of verbal and nonverbal features underlying communicative patterns. However, the strength of the association between the synchronisation of nonverbal features (movements and vocal tones) and therapeutic alliance and outcome remains unclear.ObjectivesThis meta‐analysis aimed to investigate the strength of (1) the association between nonverbal synchrony and perception of alliance reported by the patients, (2) the association between nonverbal synchrony and therapeutic outcome, and (3) the moderating role of the type of psychotherapeutic approach.MethodsThis meta‐analysis included 11 studies. Inclusion criteria were studies that utilised a quantitative measure of nonverbal synchrony in association with measures of therapeutic alliance and outcome.ResultsRandom effects model indicated that nonverbal synchrony was significantly associated with the alliance perceived by the patient (r = 0.19; 95% CI: 0.02–0.35; z = 2.18, p = 0.02); however, it was not significantly associated with the therapeutic outcome (r = 0.22; 95% CI: −0.04 to 0.47; z = 1.65, p = 0.09). No moderating effects were observed for the type of therapeutic approach.ConclusionsThese findings support the view that nonverbal synchrony is a central aspect of psychotherapy and highlight the possible interdependence between nonverbal synchrony and therapeutic alliance.