Introduction Psychology students at universities in Denmark and worldwide often receive relatively little clinical training, even though such training is crucial to job performance after graduation. Training common psychotherapeutic skills, such as being empathic and facilitating the therapeutic alliance, is critical since these skills are related to psychotherapy outcomes. In this study, a deliberate practice-based approach to student training will be compared with theoretical teaching. The main hypothesis is that deliberate practice training will result in a larger improvement in students' observer-rated interpersonal skills. Methods and analysis The TRaining of graduate students In general Psychotherapeutic Skills study has a double-centre, randomised, assessor-blinded, two-way crossover study design. About 200 graduate students from two Danish universities will be randomised into two groups, (a) deliberate practice training of common psychotherapeutic skills using role-play and Skillsetter, an online skill-building system with therapy videos or (b) theoretical teaching. Group a will first receive the experimental condition, followed by the control condition, while group b will receive the conditions in reverse order. Each condition consists of 15 hours of classroom participation and homework. The primary outcome is facilitative interpersonal skills - observer. Secondary outcomes include the facilitative interpersonal skills - self-report, the Counselor Activity Self-Efficacy Scales and the Interpersonal Reactivity Index. Outcomes will be measured at baseline (week 0), after the first condition (week 5; before the crossover, reflecting true randomisation) and after both conditions (week 10). Main outcome analyses will be performed at week 5. Several predictors of the effect of deliberate practice will be explored. Ethics and dissemination Ethical approval from university ethics boards has been obtained. All participants will be asked to provide informed consent before participation. Once completed, the study can potentially transform the training of psychotherapy in graduate education, which, ultimately, may positively influence psychotherapy outcomes (IP-IRB / 03092021). Trial registration number NCT05164497.