Behavioural treatments for depression have shown promising preliminary effects for depression in inpatient wards. However, more research is needed regarding their feasibility in psychiatric intensive care units (PICU). The aim of the current trial was to examine the feasibility of brief behavioural activation treatment for depression (BATD) in a PICU. ‘BATD added to standard care’ was compared to ‘standard care’ in a randomised controlled trial (RCT) with moderate to severely depressed inpatients. Between group differences on BDI-II (n = 19) was significant on post-test and gain-scores with strong effect sizes towards BATD, and response rates were significantly higher for participants who received BATD, with a strong effect size. Participants rated BATD as credible and acceptable in the setting. Treatment integrity was high and participant attrition was low for participants receiving BATD added to standard care. Preliminary support for BATD’s clinical significance, credibility and acceptability was found among inpatients. The main limitation was the large number of ineligible participants due to the inclusion criteria. The current study provides further support for BATD’s feasibility for treating depression among inpatients, including its administration by inpatient nursing staff.