Background: We previously reported results of a randomized phase 2 study, demonstrating a higher rate of major pathological response to durvalumab in combination with stereotactic body radiotherapy (SBRT) compared to durvalumab alone in patients with localized (stage I-IIIA) non-small cell lung cancer (NSCLC). Biomarkers of response in NSCLC are poorly understood. To address this, we evaluated sequentially collected peripheral blood mononuclear cells (PBMCs) from study participants to identify easily accessible biomarkers associated with major pathological responses. Methods: PBMCs were obtained from study participants at defined pre-treatment, peri-operative, and post-operative timepoints. We performed 25-marker spectral flow cytometric analysis of the T cell compartment in these samples and used dimensionality reduction and clustering programs to identify populations of interest. Results: Our analysis of these samples revealed populations of both CD4⁺ and CD8⁺ T cells with hallmarks of prior antigen exposure and tissue residency (CD103⁺, CCR7^-, CD45RA^-), suggesting tumor-experienced T cells circulating into the blood. Greater pre-treatment frequency of these T cell populations was associated with major pathological responses to neoadjuvant therapy. This observation was consistent when evaluating patients with major pathological responses across both treatment arms, and within the durvalumab plus SBRT group, where we had enough patients with major pathological responses. Maturation of disease-free survival data from this trial will enable us to evaluate the association of these biomarkers with long-term survival. Conclusions: Together, these data reveal an unexpected population of T cells in the peripheral blood with features of tissue-residency, which are associated with major pathological responses, and suggest that re-circulation of tumor-experienced T cells may represent a predictive biomarker for neoadjuvant treatment of NSCLC.