Intensive Short-Term Psychodynamic Therapy (ISTDP) has demonstrated promising evidence for the treatment of several Functional Neurological Disorders (FND) including dissociative seizures. However, its implementation in secondary mental health and specialist services within the English National Health Service (NHS) is scarce. The aim of this pilot study was to explore the estimates of the therapeutic effects of a 3-session course of this treatment as well as establish safety and acceptability for a complex patient group. The study followed a mixed methods case series design and recruited 18 patients from secondary adult mental health care and specialist neurology services. Participants completed self-report outcome measures at the start, at the end and 1 month following the completion of therapy. Three open-ended questions examined their therapy experiences qualitatively and these were analysed through thematic analysis. All participants who started the treatment (N = 17) completed the intervention and attendance rates were very high (95%). No serious adverse effects were observed and the CORE-OM and BSI showed improvements both at the end of the treatment and at follow-up. Healthcare utilisation was also reduced, including acute medications, A&E attendances and crisis-line usage. The results provide preliminary support for the safe use of ISTDP in this complex group of participants, but further evidence from controlled and randomized studies is warranted.