Background: Rates of aggression in inpatient secure care are higher than in other psychiatric inpatient settings. People with intellectual disabilities in secure care require adapted psychological treatments. Interpersonal art psychotherapy incorporates the use of creative art making approaches by participants, thus reducing sole reliance upon verbal interactions during psychotherapy for people who may have communication difficulties. During interpersonal art psychotherapy, participants are individually supported by their therapist to consider how they conduct relationships. This includes the influence and impact of interpersonal issues resulting in repeated patterns of conflict. The key feasibility objectives were to assess recruitment and retention rates, follow-up rates and trial procedures such as randomisation, allocation and identifying any practical or ethical problems. In addition, a preliminary ‘signal’ for the intervention was considered and an indicative sample size calculation completed. The acceptability of a potential third trial arm attentional control condition, mindful colouring-in, was assessed using four single-case design studies and a UK trial capacity survey was conducted. Methods: Adult patients with intellectual disabilities in secure care were recruited and randomised to either interpersonal art psychotherapy or delayed treatment in this multi-site study. Outcomes were assessed using weekly observations via the Modified Overt Aggression Scale and a range of self-report measures. Within study reporting processes, qualitative interviews and a survey were completed to inform trial feasibility. Results: Recruitment procedures were successful. The target of recruiting 20 participants to the trial from multiple sites was achieved within 8 months of the study opening. All participants recruited to the treatment arm completed interpersonal art psychotherapy. Between-group differences of interpersonal art psychotherapy versus the delayed treatment control showed a ‘signal’ effect-size of.65 for total scores and.93 in the verbal aggression sub-scale. There were no amendments to the published protocol. The assessment of key feasibility objectives were met and the trial procedures were acceptable to all involved in the research. Conclusion: This study suggested that a randomised controlled trial of interpersonal art psychotherapy is acceptable and feasible. Trial registration: ISRCTN14326119 (Retrospectively Registered).