Primary malignant brain tumours can have an unpredictable course, but high-grade gliomas typically have a relentlessly progressive disease trajectory. They can cause profound symptom burden, affecting physical, neurocognitive, and social functioning from an early stage in the illness. This can significantly impact on role function and on the experiences and needs of informal caregivers. Access to specialist palliative and supportive care early in the disease trajectory, for those with high-grade tumours in particular, has the potential to improve patients' and caregivers' quality of life. However, provision of palliative and supportive care for people with primary brain tumours - and their informal caregivers - is historically ill-defined and ad hoc, and the benefits of early palliative interventions have not been confirmed. It is therefore important to define the role and effectiveness of early referral to specialist palliative care services and/or the effectiveness of other interventions focused on palliating disease impact on people and their informal caregivers. This would help guide improvement to service provision, by defining those interventions which are effective across a range of domains, and developing an evidence-based model of integrated supportive and palliative care for this population. To assess the evidence base for early palliative care interventions, including referral to specialist palliative care services compared to usual care, for improving outcomes in adults diagnosed with a primary brain tumour and their carers. We conducted searches of electronic databases, CENTRAL, MEDLINE, CINAHL, Web of Science, and PsycINFO (last searched 16 November 2021). We conducted searches to incorporate both qualitative and quantitative search terms. In addition to this, we searched for any currently recruiting trials in ClinicalTrials.gov and in the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) search portal, and undertook citation tracking via Scopus. We also handsearched reference lists of potentially eligible systematic review articles to identify any other relevant studies, contacted experts in the field and searched key authors via Web of Science and searched SIGLE (System of Information on Grey Literature in Europe). We included studies looking at early referral to specialist palliative care services - or early targeted palliative interventions by other healthcare professionals - for improving quality of life, symptom control, psychological outcomes, or overall survival as a primary or secondary outcome measure. Studies included randomised controlled trials (RCTs), non-randomised studies (NRS), as well as qualitative and mixed-methods studies where both qualitative and quantitative data were included. Participants were adults with a confirmed radiological and/or histological diagnosis of a primary malignant brain tumour, and/or informal adult carers (either at individual or family level) of people with a primary malignant brain tumour. We followed standard Cochrane methodological procedures for data extraction, management, and analysis. We used GRADE to assess the certainty of the evidence for symptom control, i.e. cognitive function. We identified 9748 references from the searches, with 8337 remaining after duplicates were removed. After full-text review, we included one trial. There were no studies of early specialist palliative care interventions or of early, co-ordinated generalist palliative care approaches. The included randomised trial addressed a single symptom area, focusing on early cognitive rehabilitation, administered within two weeks of surgery in a mixed brain tumour population, of whom approximately half had a high-grade glioma. The intervention was administered individually as therapist-led computerised exercises over 16 one-hour sessions, four times/week for four weeks. Sessions addressed several cognitive domains including time orientation, spatial orientation, visual attention, logical reasoning, memory, and executive function. There were no between-group differences in outcome for tests of logical-executive function, but differences were observed in the domains of visual attention and verbal memory. Risk of bias was assessed and stated as high for performance bias and attrition bias but for selective reporting it was unclear whether all outcomes were reported. We considered the certainty of the evidence, as assessed by GRADE, to be very low. Currently there is a lack of research focusing on the introduction of early palliative interventions specifically for people with primary brain tumours, either as co-ordinated specialist palliative care approaches or interventions focusing on a specific aspect of palliation. Future research should address the methodological shortcomings described in early palliative intervention studies in other cancers and chronic conditions. In particular, the specific population under investigation, the timing and the setting of the intervention should be clearly described and the standardised palliative care-specific components of the intervention should be defined in detail.