Cognitive behaviour therapy is recommended internationally as a treatment for psychosis (targeting symptoms such as auditory hallucinations, or “voices”). Yet mental health services are commonly unable to offer such resource-intensive psychological interventions. Brief, symptom-specific and less resource-intensive therapies are being developed as one initiative to increase access. However, as access increases, so might the risk of offering therapy to clients who are not optimally disposed to engage with and benefit from therapy. Thus, it is important to identify who is most/least likely to engage with and benefit from therapy, and when. In the current study, 225 clients were assessed for suitability for a brief, 4-session, manualized, cognitive behaviour therapy-based intervention for voices (named coping strategy enhancement therapy) and 144 commenced therapy, at a transdiagnostic voices clinic based in Sussex, UK. This article reports on the value of depression, anxiety, stress, insight into the origin of voices, length of voice hearing, and demographics in the prediction of engagement and outcomes. The study found that higher levels of baseline depression, anxiety, and stress were significantly associated with poorer outcomes, especially if clients also had high levels of voice-related distress. The engagement analyses showed that levels of voice-related distress at baseline predicted dropout. These findings highlight the importance of assessing negative affect and voice-related distress prior to commencing therapy for distressing voices, to help determine if the client is suitable or ready for brief-coping strategy enhancement.