Background: Theory-based and qualitative evaluations in pilot trials of complex clinical interventions help to understand quantitative results, as well as inform the feasibility and design of subsequent effectiveness and implementation trials. Aim: To explore patient, family, clinician and volunteer (‘stakeholder’) perspectives of the feasibility and acceptability of a multicomponent non-pharmacological delirium prevention intervention for adult patients with advanced cancer in four Australian palliative care units that participated in a phase II trial, the ‘PRESERVE pilot study’. Design: A trial-embedded qualitative study via semi-structured interviews and directed content analysis using Michie’s Behaviour Change Wheel and the Theoretical Domains Framework. Setting/participants: Thirty-nine people involved in the trial: nurses ( n = 17), physicians ( n = 6), patients ( n = 6), family caregivers ( n = 4), physiotherapists ( n = 3), a social worker, a pastoral care worker and a volunteer. Results: Participants’ perspectives aligned with the ‘capability’, ‘opportunity’ and ‘motivation’ domains of the applied frameworks. Of seven themes, three were around the alignment of the delirium prevention intervention with palliative care (intervention was considered routine care; intervention aligned with the compassionate and collaborative culture of palliative care; and differing views of palliative care priorities influenced perspectives of the intervention) and four were about study processes more directly related to adherence to the intervention (shared knowledge increased engagement with the intervention; impact of the intervention checklist on attention, delivery and documentation of the delirium prevention strategies; clinical roles and responsibilities; and addressing environmental barriers to delirium prevention). Conclusion: This theory-informed qualitative study identified multiple influences on the delivery and documentation of a pilot multicomponent non-pharmacological delirium prevention intervention in four palliative care units. Findings inform future definitive studies of delirium prevention in palliative care. Australian New Zealand Clinical Trials Registry, ACTRN12617001070325; https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=373168