Comprehend, Cope, and Connect (CCC) is a third‐wave cognitive behavioural approach developed for acute mental health services. The aim of this study was to assess feasibility and acceptability of a newly developed, manualized single‐session CCC intervention delivered face‐to‐face with service users in acute and crisis psychology services in South London. The study adopted a within‐subjects pre‐post‐test design. Participants (N = 23) were recruited from five acute psychiatric wards and a crisis resolution home treatment team. Service users had a range of diagnoses of complex and severe mental health conditions, in particular mood, personality, and psychotic disorders. Feasibility data were gathered for number of times the CCC formulation was accepted, duration of CCC intervention, clinician adherence to manualised protocol, and frequency of goal‐based activity completion. Acceptability data on pre‐ and post‐CCC mood and post‐CCC helpfulness were self‐reported by participants. Findings indicated a significant increase in positive mood (large effect) and moderate–high helpfulness rating postintervention. Most participants reported goal‐based activity completion. There was high fidelity to the protocol, high percentage of acceptance of the formulation and formulation components completed, and frequent single‐session completion. Single‐session CCC appears feasible and acceptable in acute and crisis psychology services and yields formulation‐driven goal‐based activities intended to stabilize mental health crisis. High fidelity to formulation protocol suggests broader applications for single‐session CCC, for example, to support clinical staff to manage crisis situations in their work environment or to train nonpsychologist clinicians to deliver the intervention for service users. A randomized controlled trial of single‐session CCC would increase validity and generalisability of findings.