Importance: Family members of patients with severe acute brain injury (SABI) are at risk for poor psychological outcomes. Objective: To explore the utility of the early use of a palliative care needs checklist in identifying care needs of patients with SABI and family members who are at risk of poor psychological outcomes. Design, Setting, and Participants: This prospective cohort study included patients with SABI in an intensive care unit (ICU) for 2 days or more and a Glasgow Coma Scale score of 12 or lower and their family members. This single-center study was conducted at an academic hospital in Seattle, Washington, from January 2018 to June 2021. Data were analyzed from July 2021 to July 2022. Exposure: At enrollment, a 4-item palliative care needs checklist was completed separately by clinicians and family members. Main Outcomes and Measures: A single family member for each enrolled patient completed questionnaires assessing symptoms of depression and anxiety, perception of goal-concordant care, and satisfaction in the ICU. Six months later, family members assessed their psychological symptoms, decisional regret, patient functional outcome, and patient quality of life (QOL). Results: A total of 209 patient-family member pairs (family member mean [SD] age, 51 [16] years; 133 women [64%]; 18 Asian [9%], 21 Black [10%], 20 [10%] Hispanic, and 153 White [73%] participants) were included. Patients had experienced stroke (126 [60%]), traumatic brain injury (62 [30%]), and hypoxic-ischemic encephalopathy (21 [10%]). At least 1 need was identified for 185 patients or their families (88%) by family members and 110 (53%) by clinicians (κ = -0.007; 52% agreement). Symptoms of at least moderate anxiety or depression were present in 50% of family members at enrollment (87 with anxiety and 94 with depression) and 20% at follow-up (33 with anxiety and 29 with depression). After adjustment for patient age, diagnosis, and disease severity and family race and ethnicity, clinician identification of any need was associated with greater goal discordance (203 participants; relative risk = 1.7 [95% CI, 1.2 to 2.5]) and family decisional regret (144 participants; difference in means, 17 [95% CI, 5 to 29] points). Family member identification of any need was associated with greater symptoms of depression at follow-up (150 participants; difference in means of Patient Health Questionnaire-2, 0.8 [95% CI, 0.2 to 1.3] points) and worse perceived patient QOL (78 participants; difference in means, -17.1 [95% CI, -33.6 to -0.5] points). Conclusions and Relevance: In this prospective cohort study of patients with SABI and their families, palliative care needs were common, although agreement on needs was poor between clinicians and family members. A palliative care needs checklist completed by clinicians and family members may improve communication and promote timely, targeted management of needs.