Untreated psychosis can have a devastating impact on individuals and their families. Recommended therapies are underutilised. Attachment theory provides a framework to understand intra- and interpersonal responses to threat cues, such as voices and paranoia, which affect recovery. This is the first study to test a coherent set of theory-driven predictions about the impact of attachment style on people's ability to manage distress associated with psychosis, and seek help effectively. We used a cross-sectional design to examine the impact of attachment style on emotional regulation, help-seeking intentions, service engagement, and clinical and recovery outcomes in people with psychosis. We recruited a total of 65 participants with psychosis from community and NHS pathways. Participants completed standardized measures of predictor and dependent variables at one-time point. Regression analyses showed that insecure attachment (anxious and avoidant) predicted more use of unhelpful emotional regulation strategies, less help-seeking, and poorer clinical and recovery outcomes, with medium to large effects (p < 0.05). We found no effects for service engagement. Attachment style predicts intra- and interpersonal responses to threat in psychosis, and may partially account for the considerable variation in engagement with recommended therapies, and longer-term outcomes. Routine assessment of attachment at initial service contact would identify people likely to struggle to seek and accept therapeutic interventions, who may in turn benefit from attachment-congruent engagement efforts.