Background: PD-L1 expression has been established as a positive predictive biomarker for immune checkpoint inhibition in advanced non-small cell lung cancer (NSCLC). We hypothesize that PD-L1 serves as a negative predictive biomarker of chemotherapy in squamous NSCLC in contrast to non-squamous NSCLC. Methods: Phase III randomized trials that investigated PD-L1 expression as a biomarker in advanced squamous NSCLC at first-line were identified and included through a systematic search of Embase and PubMed from inception until 24^th September, 2022. To investigate the anti-thesis, trials that reported PD-L1 stratified KM plots in non-squamous NSCLC were evaluated too. Only trials that reported PD-L1 stratified KM curves of chemotherapy arms were included. A graphical reconstructive algorithm was used to retrieve survival data from reported Kaplan-Meier (KM) curves. Pooled survival analyses for progression-free and overall survival (PFS, OS) were conducted with Cox proportional hazard models with a shared-frailty term incorporated to account for inter-study differences. Results: Five phase III randomized trials (2 squamous NSCLC and 3 non-squamous NSCLC) reporting PD-L1 stratified KM plots of patients treated with first-line chemotherapy were included. In patients with squamous histology, PD-L1 expression negatively predicted for chemotherapy benefit – patients with higher PD-L1 expression were at a higher risk of tumour progression (PD-L1 ≥50% [n = 187] vs PD-L1 < 1% [n = 247]: HR = 1.474, 95%-CI: 1.171-1.855, p < 0.001; PD-L1 ≥50% [n = 187] vs PD-L1 1-49% [n = 239]: HR = 1.300, 95%-CI: 1.033-1.625, p = 0.025). Conversely, in patients with non-squamous histology, no significant differences in tumour progression was shown between PD-L1 subgroups (PD-L1 ≥50% [n = 137] vs PD-L1 < 1% [n = 242]: HR = 1.238, 95%-CI: 0.919-1.667, p = 0.160; PD-L1 ≥50% [n = 137] vs PD-L1 1-49% [n = 199]: HR = 0.958, 95%-CI: 0.714 -1.285, p = 0.780). No significant difference in OS was found between PD-L1 subgroups dichotomized at 1% & 50% among patients with squamous histology. In contrast, in patients with non-squamous histology, PD-L1 was a positive biomarker for chemotherapy benefit – patients with higher PD-L1 were at a lower risk of mortality (PD-L1 ≥50% [n = 40] vs PD-L1 < 1% [n = 150]: HR = 0.523, 95%-CI: 0.316-0.865, p = 0.012). Conclusions: These findings suggest that PD-L1 expression is uniquely a negative predictor for tumour progression in advanced squamous NSCLC treated with first-line chemotherapy.