Purpose The Carer Support Needs Assessment Tool Intervention (CSNAT-I) has shown positive effects in the Danish specialised palliative care (SPC) setting. Here, we explore the process, content, and experiences of delivering the CSNAT-I. Methods Data were collected during a stepped wedge cluster randomised controlled trial investigating the impact of the CSNAT-I in the Danish SPC setting in 2018-2019. Data were obtained from the CSNAT (tool) completed by caregivers, from health care professionals' (HCPs') written documentation of the CSNAT-I, and from semi-structured interviews with HCPs. Results The study population consisted of the 130 caregivers receiving a first CSNAT-I within 13 days of study enrolment, the 93 caregivers receiving a second CSNAT-I 15-27 days after enrolment, and the 44 HCPs delivering the intervention. Top three domains of unmet caregiver support needs reported in the CSNAT-I were: "knowing what to expect in the future," "dealing with feelings and worries," and "understanding the illness." These domains together with "knowing who to contact if concerned" and "talking to the patient about the illness" were also the domains most frequently prioritised for discussion with HCPs. According to HCPs, most often support delivered directly by HCPs themselves during the actual contact (e.g., listening, advice, information) was sufficient. Overall, HCPs experienced the CSNAT-I as constructive and meaningful, and difficulties in delivering the intervention were rarely an issue. Conclusion The support needs reported by caregivers confirm the relevance of the CSNAT-I. HCPs' overall experiences of the clinical feasibility and relevance of the CSNAT-I were very positive. ClinicalTrials.gov ID: NCT03466580. Date of registration: March 1, 2018.