Objectives Use of immune checkpoint inhibitors as first-line treatment for advanced (stage IIIB/IV) non-small cell lung cancer (NSCLC) remains controversial. Clinical trials comparing single-drug immunotherapy (IO) with immunotherapy plus chemotherapy (IC) are lacking. We aimed to compare the efficacy of IO alone with that of IC as first-line treatment for advanced NSCLC. Design Systematic review. Data sources PubMed, the Cochrane Library and Embase for related studies on NSCLC; ClinicalTrials.gov, American Society of Clinical Oncology Meeting Library and World Conference on Lung Cancer for relevant conference abstracts (to July 2019). Eligibility criteria Articles meeting the following criteria were selected: (1) randomised controlled trials on NSCLC treatment, (2) all individuals in the studies had not received treatment previously and (3) research on IO monotherapy using programmed death-1/programmed death ligand-1 (PD-L1) inhibitors or IC. Data extraction and synthesis After reading the original literature, two reviewers independently extracted the relevant information. The primary outcomes were progression-free survival (PFS), overall survival (OS) and objective response rate (ORR). We also extracted data on treatment-related adverse events and immune-related adverse events (irAEs). Results Overall, 10 randomised controlled clinical trials (n=5765) were included. As first-line treatment for advanced NSCLC, IC tended to yield better PFS, OS and ORR than did IO. Furthermore, IC yielded significantly better PFS than IO when tumour PD-L1 expression was at least 50% (HR: 1.81, 95% CI: 1.18 to 2.78) and yielded a better OS and PFS when tumour PD-L1 expression was at least 1%; IO resulted in fewer adverse events than did IC. However, the incidence of irAEs was higher for IO than for IC. Conclusions The findings of the indirect comparison indicate that IC as first-line treatment for advanced NSCLC is significantly more effective than IO in patients with PD-L1 expression in at least 50% of tumour cells.