BACKGROUND: It is notoriously challenging to deliver psychosocial interventions on acute mental health wards. This paper presents an ethnographic observational study which captured how ward and staff processes impacted on the delivery of a psychosocial intervention called TULIPS (Talk, Understand and Listen for Inpatient Settings). Although the paper is focused on one specific intervention, the findings have implications for the delivery of other psychosocial interventions within acute mental health settings. METHOD: We carried out participant observation across 6 case studies wards all participating in the intervention arm of a cluster randomised controlled trial evaluating the TULIPS intervention compared to treatment as usual. Trained researchers observed ward environments, activities and social interactions taking detailed field notes which were later subject to thematic analysis. RESULTS: Four themes were generated from field notes relating to aspects of the ward culture and staff behaviours which were barriers or facilitators to the delivery of the TULIPS intervention. Theme one highlighted how the person-centred nature of the TULIPS model was at odds with the pre-existing culture of the wards which favoured blanket rules. Theme two highlighted how staff prioritised task-oriented quantifiable activities which clashed with the emphasis the TULIPS model placed on relationship building. The third theme highlighted the presence of conflict between different groups of staff working on the ward and theme four highlighted the stressful nature of the ward environment which drove staff to seek refuge from patient facing activities including TULIPS related activities. CONCLUSIONS: In order to successfully engage with the delivery of psychosocial interventions on acute mental health wards, staff need access to supportive leadership which champions psychological interventions, as well as training, supervision and support systems which value the demanding nature of working on mental health inpatient wards.