Background: Medicaid expansion under the Affordable Care Act is associated with gains in health insurance coverage and a shift towards earlier stage diagnosis among patients with cancer. However, the association between Medicaid expansion and cancer mortality has not been well characterized. The aim of this study was to evaluate the association of Medicaid expansion with changes in early mortality, defined as death within 30 days after major NSCLC surgery, among adults discharged following major surgery for non-small cell lung cancer (NSCLC), a setting where access to care is a major determinant of death. Methods: Of the 11,627 patients selected from the National Cancer Database who were aged 45-64 (more likely to be diagnosed and die from NSCLC and not age-eligible for Medicare coverage) and were discharged from the hospital following major surgery for treatment of NSCLC between 2009 and 2018, 7,294 patients lived in expansion states and 4,333 lived in non-expansion states. Differences-in-differences (DD) analyses were used to evaluate the impact of Medicaid expansion on early mortality pre-(2009- 2013) and post-ACA (2014- 2018). Results: Early mortality among patients discharged from the hospital following NSCLC surgery statistically significantly decreased from 2.4% pre-ACA to 0.8% post-ACA among patients in Medicaid expansion states (1.6 percentage point decrease, p <.0001), but not in patients living in non-expansion states (from 2.1% to 1.6%, p = 0.2), leading to a DD of 1.1 percentage points (95% Confidence Interval = 0.1, 2.1; p = 0.03). Conclusions: This study found a decrease in early mortality following hospital discharge after NSCLC surgery post-ACA among patients living in Medicaid expansion states and no change in patients residing in non-expansion states. Medicaid expansion may be an effective strategy for improving access to care and cancer outcomes among older adults who are not age-eligible for Medicare.