Abstract Purpose: Limited long-term data are available on immune checkpoint inhibitor use in patients with advanced esophageal squamous cell carcinoma (ESCC). We report 3-year follow-up data from our study of nivolumab versus chemotherapy (paclitaxel or docetaxel) in patients with previously treated ESCC. Patients and Methods: ATTRACTION-3 was a randomized, multicenter, open-label, phase III trial. Overall survival (OS), time from randomization to death from any cause, was the primary endpoint. An exploratory subanalysis assessed OS according to the best overall response (BOR) with and without landmark at 4 months. Results: Of the enrolled patients, 210 received nivolumab and 209 received chemotherapy. With a minimum follow-up of 36.0 months, OS was longer in the nivolumab versus the chemotherapy group (median, 10.9 vs. 8.5 months; HR, 0.79; P = 0.0264), with 3-year OS rates of 15.3% and 8.7%, respectively. The median OS was longer with nivolumab versus chemotherapy irrespective of the BOR (complete response/partial response: 19.9 vs. 15.4 months; stable disease: 17.4 vs. 8.8 months; and progressive disease: 7.6 vs. 4.2 months). Grade 3 or higher treatment-related adverse events were reported in 40 patients (19.1%) in the nivolumab group and 133 patients (63.9%) in the chemotherapy group. Conclusions: Nivolumab as second-line therapy demonstrated clinically meaningful long-term improvement in OS compared with chemotherapy in previously treated patients with advanced ESCC. The OS was consistently improved in the nivolumab group compared with the chemotherapy group regardless of BOR. Nivolumab was well tolerated over the 3-year follow-up. See related commentary by Yoon et al., p. 3173