Background: The preferred treatment for early-stage non-small cell lung cancer remains surgical resection with the consideration of adjuvant chemotherapy for tumors with certain high-risk features. It is commonly cited that such treatments confer a meager 5% 5-year survival benefit compared to observation alone. We sought to reassess the benefit of adjuvant chemotherapy using modern, real-world datasets. Methods: We performed a retrospective cohort study using a dataset from the National Cancer Database. All patients with early-stage stage NSCLC (3-5cm, node-negative) who would be eligible for adjuvant chemotherapy based on National Comprehensive Cancer Network guidelines were included (i.e., presence of at least 1 high-risk feature). High-risk clinical and pathologic features were defined as poor differentiation, tumor size (≥4cm), non-anatomic wedge resection, inadequate lymph node evaluation, vascular invasion, and visceral pleural involvement. We employed average treatment effect on the treated (ATT) weighting to match patients with similar demographic, tumor, and treatment-related variables to compare outcomes between chemotherapy versus observation groups. The primary outcome was overall survival. These findings were further validated in an independent cohort from the US Veteran Health Administration (VHA). Results: The study included 10,812 patients with early-stage NSCLC who had at least 1 high-risk feature. The frequencies of high-risk features were as follows: tumor size ≥4cm (n = 3,271, 30.3%), poor differentiation (n = 9,454, 87.4%), visceral-pleural invasion (n = 2,542, 23.5%), vascular invasion (n = 1,742, 16.11%), non-anatomic wedge resection (n = 781, 7.2%), and inadequate nodal sampling (n = 6,306, 58.3%). Despite the presence of high-risk features, only 1,427 (13.2%) patients received adjuvant chemotherapy. In the ATT weighted analysis, 1,261 (49.7%) patients received adjuvant chemotherapy and 1,278 (50.3%) patients received observation. The 5-year overall survival was 70.0% (95% CI 67.1-72.7) in the chemotherapy group versus 62.0% (95% CI 60.2-63.7%) in the observation group (absolute 5-year survival difference 8.0%). In the VHA cohort, 11.3% of patients received adjuvant chemotherapy. Similarly, the 5-year overall survival was 64.0% (95% CI 51.4-74.2) in the chemotherapy group versus 56.2% (95% CI 48.3-63.4) in the observation group (absolute 5-year survival difference 7.8%). Conclusions: These data suggest a notably larger benefit of adjuvant chemotherapy in eligible patients with high-risk clinical pathologic features compared to commonly cited statistics. With the addition of more robust treatment options in early-stage disease, adherence to adjuvant and neoadjuvant treatment guidelines may disproportionately improve early-stage NSCLC outcomes following curative-intent resection.