Background: Despite the emergence of programmed death 1/programmed death-ligand 1 (PD-1/PD-L1) inhibitors in the treatment of non-small cell lung cancer (NSCLC) patients with brain metastases (BMs), knowledge gaps remain regarding the impact and timing of cranial radiotherapy for patients receiving anti-PD-1/PD-L1 therapy. Methods: Data were collected from 461 consecutive patients who received anti-PD-1/PD-L1 therapy for metastatic NSCLC at three institutions between June 2017 and September 2020. Intracranial progressive disease (PD) at the original disease sites, new sites, or both sites were classified as original-site PD (OPD), new-site PD (NPD), and original-and-new-site PD (ONPD), respectively. Patients with baseline BMs were categorized based on whether they received upfront cranial radiotherapy (uCRT) at any time point between the introduction of anti-PD-1/PD-L1 therapy and the first subsequent progression. Results: Of the 461 patients enrolled, 110 (23.9%) had BMs at baseline. The presence of BMs did not show independent prognostic value for progression-free survival (PFS) or overall survival (OS). During a median follow-up of 13.2 months, 96 patients with BMs developed PD, of whom 53 (55.2%) experienced intracranial PD. OPD, NPD, and ONPD were observed in 50.9%, 18.9%, and 30.2% of patients, respectively. Patients who received uCRT exhibited a longer median OS than those with BMs who did not receive uCRT (25.4 vs. 14.6 months, HR: 0.52, 95% CI: 0.29-0.91, P=0.041); this survival advantage was more prominent in patients with 1-4 BMs (median OS, 25.4 vs. 17.0 months, HR: 0.42, 95% CI: 0.22-0.81, P=0.024), and uCRT was independently associated with OS among these patients. Conclusions: The presence of BMs at baseline was not associated with poorer OS in patients with metastatic NSCLC treated with anti-PD-1/PD-L1 therapy. Intracranial progression on PD-l/PD-L1 inhibitors predominately occurred at the original BM sites. The use of uCRT may improve OS, especially in NSCLC patients with 1-4 BMs.