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.