IntroductionFunctional cognitive disorder (FCD) is seen increasingly in clinics commissioned to assess cognitive disorders. Patients report frequent cognitive, especially memory, failures. The diagnosis can be made clinically, and unnecessary investigations avoided. While there is some evidence that psychological treatments can be helpful, they are not routinely available. Therefore, we have developed a brief psychological intervention using the principles of acceptance and commitment therapy (ACT) that can be delivered in groups and online. We are conducting a feasibility study to assess whether the intervention can be delivered within a randomised controlled trial. We aim to study the feasibility of recruitment, willingness to be randomised to intervention or control condition, adherence to the intervention, completion of outcome measures and acceptability of treatment.Methods and analysisWe aim to recruit 48 participants randomised 50:50 to either the ACT intervention and treatment as usual (TAU), or TAU alone. ACT will be provided to participants in the treatment arm following completion of baseline outcome measures. Completion of these outcome measures will be repeated at 8, 16 and 26 weeks. The measures will assess several domains including psychological flexibility, subjective cognitive symptoms, mood and anxiety, health-related quality of life and functioning, healthcare utilisation, and satisfaction with care and participant-rated improvement. Fifteen participants will be selected for in-depth qualitative interviews about their experiences of living with FCD and of the ACT intervention.Ethics and disseminationThe study received a favourable opinion from the South East Scotland Research Ethics Committee 02 on 30 September 2022 (REC reference: 22/SS/0059). HRA approval was received on 1 November 2022 (IRAS 313730). The results will be published in full in an open-access journal.Trial registration numberISRCTN12939037.