Importance There remains an unmet need to improve clinical outcomes in patients with recurrent or metastatic squamous cell carcinoma of the head and neck (R/M SCCHN). Objective To evaluate clinical benefit of first-line nivolumab plus ipilimumab vs nivolumab alone in patients with R/M SCCHN. Design, Setting, and Participants The CheckMate 714, double-blind, phase 2 randomized clinical trial was conducted at 83 sites in 21 countries between October 20, 2016, and January 23, 2019. Eligible participants were aged 18 years or older and had platinum-refractory or platinum-eligible R/M SCCHN and no prior systemic therapy for R/M disease. Data were analyzed from October 20, 2016 (first patient, first visit), to March 8, 2019 (primary database lock), and April 6, 2020 (overall survival database lock). Interventions Patients were randomized 2:1 to receive nivolumab (3 mg/kg intravenously [IV] every 2 weeks) plus ipilimumab (1 mg/kg IV every 6 weeks) or nivolumab (3 mg/kg IV every 2 weeks) plus placebo for up to 2 years or until disease progression, unacceptable toxic effects, or consent withdrawal. Main Outcomes and Measures The primary end points were objective response rate (ORR) and duration of response between treatment arms by blinded independent central review in the population with platinum-refractory R/M SCCHN. Exploratory end points included safety. Results Of 425 included patients, 241 (56.7%; median age, 59 [range, 24-82] years; 194 males [80.5%]) had platinum-refractory disease (nivolumab plus ipilimumab, n = 159; nivolumab, n = 82) and 184 (43.3%; median age, 62 [range, 33-88] years; 152 males [82.6%]) had platinum-eligible disease (nivolumab plus ipilimumab, n = 123; nivolumab, n = 61). At primary database lock, the ORR in the population with platinum-refractory disease was 13.2% (95% CI, 8.4%-19.5%) with nivolumab plus ipilimumab vs 18.3% (95% CI, 10.6%-28.4%) with nivolumab (odds ratio [OR], 0.68; 95.5% CI, 0.33-1.43; P = .29). Median duration of response for nivolumab plus ipilimumab was not reached (NR) (95% CI, 11.0 months to NR) vs 11.1 months (95% CI, 4.1 months to NR) for nivolumab. In the population with platinum-eligible disease, the ORR was 20.3% (95% CI, 13.6%-28.5%) with nivolumab plus ipilimumab vs 29.5% (95% CI, 18.5%-42.6%) with nivolumab. The rates of grade 3 or 4 treatment-related adverse events with nivolumab plus ipilimumab vs nivolumab were 15.8% (25 of 158) vs 14.6% (12 of 82) in the population with platinum-refractory disease and 24.6% (30 of 122) vs 13.1% (8 of 61) in the population with platinum-eligible disease. Conclusions and Relevance The CheckMate 714 randomized clinical trial did not meet its primary end point of ORR benefit with first-line nivolumab plus ipilimumab vs nivolumab alone in platinum-refractory R/M SCCHN. Nivolumab plus ipilimumab was associated with an acceptable safety profile. Research to identify patient subpopulations in R/M SCCHN that would benefit from nivolumab plus ipilimumab over nivolumab monotherapy is warranted. Trial Registration ClinicalTrials.gov Identifier: NCT02823574