Abstract Purpose: Double inhibition of epidermal growth factor receptor (EGFR) using a tyrosine kinase inhibitor plus a monoclonal antibody may be a novel treatment strategy for non–small cell lung cancer (NSCLC). We assessed the efficacy and toxicity of afatinib + cetuximab versus afatinib alone in the first-line treatment of advanced EGFR-mutant NSCLC. Patients and Methods: In this phase II, randomized, open-label study, patients with stage III/IV EGFR-positive NSCLC were randomly assigned (1:1) to receive afatinib (group A) or afatinib + cetuximab (group A + C). Oral afatinib 40 mg was given once daily; cetuximab 250 mg/m² was administered intravenously on day 15 of cycle 1, then every 2 weeks at 500 mg/m² for 6 months. The primary endpoint was time to treatment failure (TTF) rate at 9 months. Exploratory analysis of EGFR circulating tumor DNA in plasma was performed. Results: Between June 2016 and November 2018, 59 patients were included in group A and 58 in group A + C. The study was ended early after a futility analysis was performed. The percentage of patients without treatment failure at 9 months was similar for both groups (59.3% for group A vs. 64.9% for group A + C), and median TTF was 11.1 (95% CI, 8.5–14.1) and 12.9 (9.2–14.5) months, respectively. Other endpoints, including progression-free survival and overall survival, also showed no improvement with the combination versus afatinib alone. There was a slight numerical increase in grade ≥3 adverse events in group A + C. Allele frequency of the EGFR gene mutation in circulating tumor DNA at baseline was associated with shorter PFS, regardless of the treatment received. Conclusions: These results suggest that addition of cetuximab to afatinib does not warrant further investigation in treatment-naïve advanced EGFR-mutant NSCLC.