Background: The Carer Support Needs Assessment Tool intervention (CSNAT-I) has been shown to improve end-of-life care support for informal caregivers. This study investigated the impact of the CSNAT-I on caregivers of patients recently enrolled in specialised palliative care (SPC) at home in Denmark. Methods: A stepped-wedge cluster randomised controlled trial with nine clusters (ie, SPC teams). Outcome measures were collected using caregiver questionnaires at baseline (T0) and 2-week (T1) and 4-week (T2) follow-up. Results: A total of 437 caregivers were enrolled (control group, n=255; intervention group, n=182). No intervention effect was found on the primary outcome, caregiver strain at T1 (p=0.1865). However, positive effects were found at T1 and T2 on attention to caregivers' well-being (p<0.0001), quality of information and communication (p<0.0001), amount of information (T1: p=0.0002; T2: p<0.0001), involvement (T1: p=0.0045; T2: p<0.0001), talking about greatest burdens (p<0.0001) and assistance in managing greatest burdens (p<0.0001). The effect sizes of these differences were medium or large and seemed to increase from T1 to T2. At T1, positive effects were found on distress (p=0.0178) and home care responsibility (p=0.0024). No effect was found on the remaining outcomes. Conclusion: Although no effect was found on caregiver strain, the CSNAT-I showed positive effects on caregiver distress, home care responsibility and key outcomes regarding caregivers' experience of the interaction with healthcare professionals. Trial registration number: NCT03466580.