Background: Multiple clinical studies have shown that adoptive cell transfer (ACT) of autologous tumor-infiltrating lymphocytes (TIL) is remarkably effective in melanoma patients. Non-small cell lung cancer (NSCLC) shares similarities with melanoma in terms of mutational burden and sensitivity to immune checkpoint inhibitors. We therefore sought to test whether TIL ACT may represent a viable option for the treatment of NSCLC patients. We utilized tissue collected from patients enrolled on the prospective ImmunogenomiC prOfiling of Non-small cell lung cancer (ICON) study. Methods: TIL and tissue-infiltrating lymphocytes were expanded ex vivo from 97 freshly resected early-stage localized NSCLC tumors and 39 matched uninvolved lung tissues. Growth and functional characteristics of TIL were assessed via flow cytometry, TIL-tumor reactivity assays, and analysis of TCRβ sequencing data. Results: NSCLC showed an increased proportion of CD3⁺ lymphocytes within the tumor-infiltrating leukocyte component as compared to matched normal lung tissue. The TIL compartment included a suppressed CD8⁺ T cell subset expressing significantly higher levels of PD-1 and lacking cytolytic potential compared to T cells expanded from normal tissue. TIL contained a higher proportion of proliferating (Ki67⁺) CD8⁺CD103⁺ tissue-resident memory (T_RM) cells expressing activation markers such as CTLA4, LAG3, PD1 and ICOS, and increased CD4⁺ Tregs. Despite a highly immunosuppressive environment, TIL expansion was achieved with a success rate of 68% (n = 97) but appeared hindered in patients undergoing neoadjuvant chemotherapy treatment prior to surgery (56.2%, n = 16 vs 72.5% success rate in therapy-naïve patients). In addition, expansion efficiency (number expanded and time of culture) of TIL and matched lung residing lymphocytes were significantly associated (r = 0.379, p = 0.017, n = 39). Importantly, expanded CD8⁺ TIL products were oligoclonal and showed reactivity toward autologous tumors. Conclusions: Although NSCLC TIL are functionally inhibited in vivo they can be successfully expanded ex vivo and demonstrate recognition of autologous tumor cells. These data suggest that TIL can potentially be used for adoptive T cell-based immunotherapy in NSCLC.