Objectives. The aim of the current study was to assess the feasibility, safety, and effectiveness of a newly developed Acceptance and Commitment Therapy (ACT) intervention developed specifically to address the unique context of pregnancy and parenthood. The intervention was delivered to women accessing a specialist Perinatal Community Mental Health Service (PCMHS). Design. An open-label pilot study was conducted of an 8-week, group-delivered ACT intervention targeting women with moderate-to-severe mood and/or anxiety disorders during pregnancy and/or postpartum. Methods. Outcomes included session attendance rates, dropout rates, crisis/inpatient service use, and standardized symptom scales. Participant's responses to open-ended questions containedin an end of therapy questionnairewereanalysedusing thematic analysis. Results. Seventy-four women were referred to the intervention with 65 (88%) completing treatment. The median number of sessions attended was 7. No women required input from crisis/inpatient services. All reported finding the intervention helpful. The implementation of ACT in daily life, therapist support, and group processes were cited as helpful aspects of the intervention. At post-treatment, there was a significant reduction in global distress (d = 0.99) and depressive symptoms (d = 1.05), and an increase in psychological flexibility (d = 0.93). On the secondary outcome of global distress, 38% of women were classified as recovered, 31% had reliably improved, 27% remained the same, and 4% had reliably deteriorated. Conclusions. The delivery of ACT in a routine practice setting is feasible, safe, and effective. A randomized control trial (RCT) is needed to establish the efficacy and costeffectiveness of this group-delivered ACT intervention. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.