Background: Violent and aggressive incidents are common within mental health settings and are often managed using high-risk physical interventions such as restraint and seclusion. De-escalation is a first-line technique to manage conflict behaviours and prevent violence and aggression. There is limited research into the use of de-escalation in high-secure settings. This study investigated staff, patient and carer perspectives on the barriers and facilitators to using de-escalation for conflict behaviours.Methods: Semi-structured individual interviews (n=12) and focus groups (n=3) were conducted with eight patients, four carers and twenty-five staff members in a high-secure hospital in England. Interviews and focus groups were informed by the theoretical domains framework and were digitally recorded, transcribed verbatim and analysed using framework analysis and the COM-B behaviour change model. Results: Four themes and 15 sub-themes (barriers and facilitators) were identified. Themes related to capabilities (building relationships: knowing the patient and knowing yourself), opportunities (filling the void: challenges within the high-security environment; dynamic relationships) and motivation (keeping everyone safe). Strong staff-patient therapeutic relationships underpinned by trust, fairness, consistency and an awareness of the trauma-aggression link were considered key to successful de-escalation. Specific psychological and interpersonal skills including empathy, respect, reassurance, sincerity, genuine concern and validation of the patient perspective are needed to achieve this. Barriers related to the physical environment; organisational resources, practices and systems; staff traumatisation; hierarchical and punitive attitudes towards patient care, and an insufficient understanding of psychiatric diagnoses, especially personality disorder. It was apparent across themes that fear, which was experienced by both staff and patients, was a driver for many behaviours. Conclusions: This work has identified organizational and behaviour change targets for interventions seeking to reduce violence and restrictive practices through the use of de-escalation in high-secure hospitals. The potential for, and occurrence of, violence in such settings is high and leads to fear in patients and staff. The factors which promote fear in each group should be addressed in de-escalation training.