Abstract Objectives Few data are available regarding the functional prognosis of adults with primary central nervous system vasculitis (PCNSV). We developed and validated a prognostic model for 12-month functional independence in adults with PCNSV. Methods We conducted a multicentre, international cohort study of adults with PCNSV (COVAC’). The primary end point was functional independence 12 months after the start of corticosteroids or immunosuppressants, defined as a modified Rankin Scale of 0–2. We identified baseline features independently associated with functional independence using multivariable analyses. We assessed discrimination using AUC-ROC and externally validated the model in a geographically distinct, single-centre cohort from India. Results Among the 206 patients included with PCNSV (mean age: 48 years; 41% female), 67 (33%) were diagnosed based on a positive biopsy. At 12 months, 135 (66%) patients were functionally independent and 12 (6%) had died. Favourable prognostic factors were ≥1 intracranial stenosis on CT- or MR-angiogram (OR = 2.99, 95% CI: 1.23–7.68) and headache (OR = 2.67, 95% CI: 1.31–5.59). Unfavourable prognostic factors were an altered level of consciousness (OR = 0.09, 95% CI: 0.02–0.31), ≥1 acute brain infarct (OR = 0.12, 95% CI: 0.04–0.33) and cognitive impairment (OR = 0.22, 95% CI: 0.10–0.46). A prognostic model including these five variables had an AUC of 0.80 (95% CI: 0.74–0.87) in the derivation cohort and 0.67 (95% CI: 0.54–0.81) in the validation cohort. Conclusions Baseline clinical and imaging variables may predict 12-month functional independence in adults with PCNSV. These results may support physicians in prognostication and risk stratification of adults with PCNSV.