Background This study's initial results revealed significant decreases in treatment-related esophagitis and pneumonitis cases in patients with thoracic esophageal squamous cell carcinoma (ESCC) treated with involved-field irradiation (IFI), compared to elective nodal irradiation (ENI). This report outlines the long-term trial results, specifically; overall survival (OS), progression-free survival (PFS), metastasis-free survival (MFS), and locoregional progression-free survival (LRFS). Materials and Methods Stage II-III thoracic ESCC patients were assigned randomly, in a 1:1 ratio, into either the ENI or IFI arm. Radiation therapy was delivered once a day in 1.8-2.0 Gy fractions to a total dose of 60.0-66.0 Gy to the gross tumor volume and 50.0-54.0 Gy to the clinical target volume. The primary endpoints were acute treatment-related esophagitis and pneumonitis. The results for the primary endpoints were previously published in 2018. In this article, we analyzed the secondary endpoints including PFS, LRFS, MFS, and OS. Results Between April 2012 and October 2016, 228 patients from nine participating centers in China were enrolled into this study and randomly assigned to two treatment groups. For ENI and IFI groups, respectively, the results showed similarity and were as follows: median PFS (20.3 months vs 21.4 months), OS (32.5 months vs 34.9 months), MFS (28.2 months vs 26.0 months), and LRFS (25.0 months vs 26.6 months). In particular, respective OS rates in the ENI and IFI groups were 84.6% and 82.5% after 1 year, 45.1% and 48.7% after 3 years, and 29.8% and 30.7% at 5 years. PFS rates after 1, 3, and 5 years were 58.9%, 34.2%, and 26.9%, respectively, in the ENI arm compared to 64.4%, 30.8%, and 27.7%, respectively, in the IFI arm. Multivariate analysis identified clinical stage and tumor responses as independent predictors of OS. Meanwhile, tumor location, cStage, and tumor response were identified as independent factors influencing PFS. Conclusion IFI was associated with similar survival as ENI in patients with thoracic ESCC, suggesting that IFI is an acceptable treatment method for thoracic ESCC.