ObjectiveWith a lack of experimental designs in psychotherapy/counselling process research, evidence is limited regarding which therapeutic style is helpful for which patient and the role of expectations. Therefore, the aim of this experimental study was to manipulate the therapeutic style and clients' expectations towards psychological counselling and investigate their effects on counselling outcome.MethodEighty healthy participants (74% female, Mage = 31.2 years, SDage = 12.21) received a single counselling session focussing on interpersonal conflicts. We defined two therapeutic styles (relationship‐focussed vs. problem‐focussed) based on the interpersonal circumplex, and participants were led to believe they would receive one of the two styles. In the actual counselling session, they received either the expected or the contrary, resulting in a 2 x 2 design. Primary outcome rated by participants was subjective impairment caused by the conflict 2 weeks after the session; secondary outcomes were satisfaction with the session and perceived working alliance.ResultsThe successful implementation of the proposed therapeutic styles was confirmed by adherence ratings (U = 25.50, p < 0.001) and ratings of counsellors’ behaviour in the circumplex model (p < 0.001) for the friendly and hostile dimensions. Impairment was significantly reduced 2 weeks after the counselling session, but this effect was dependent on neither the therapeutic style, clients' expectations, nor their interaction.DiscussionThe study provides the first evidence that a single counselling session appears to be effective in alleviating impairment caused by an interpersonal conflict, independent of the counselling style and client expectations. The novel experimental design provides a basis for further process research in psychological counselling and psychotherapy.