Purpose Immune checkpoint inhibitors are one of the most effective treatments available in advanced non-small cell lung cancer. However, at present, there are no clinical or analytical biomarkers that define which patients benefit with certainty from these treatments. In our study, we evaluated whether excess weight could be a good predictive biomarker of benefit from these drugs. Methods We studied a population of 79 patients, divided into a study group with 39 patients diagnosed with non-small cell lung cancer treated with immunotherapy and 40 patients in a control group, diagnosed with different advanced cancers, treated with non-immunotherapy treatment. We analyzed according to the presence of excess weight or not, the treatment’s outcome in the study group and in the control group (objective response, and progression-free and overall survival). Results In our study, we detected a better response rate to immunotherapy in patients with excess weight (62.50 vs 26.08%, OR 4.72, p  = 0.02), and a better median progression-free survival (14.19 vs 5.03 months, HR 0.50, p  = 0.058) and median overall survival (33.84 months vs 20.76 months, HR 0.43, p  = 0.01) in the study group. These findings were specific to the immunotherapy group since in the control group, with patients who did not receive immune checkpoint inhibitors, these findings were not found. Conclusion Our study suggests that patients with excess weight who receive anti-PD-1 immune checkpoint inhibitors diagnosed with non-small cell lung cancer have a better outcome. This effect is specific to patients receiving immunotherapy.