Background: Chronic rhinosinusitis with nasal polyps (CRSwNP) and type 2 asthma share the same inflammatory pathophysiology and are frequent comorbidities. Dupilumab, a fully human monoclonal antibody, blocks the shared receptor component for interleukin 4 and interleukin 13, which are key and central drivers of type 2 inflammation. Objective: We report the effect of dupilumab vs placebo on outcome measures of the upper and lower airways and health-related quality of life (HRQoL) in the pooled population of patients with CRSwNP and comorbid asthma from the phase 3 SINUS-24 (NCT02912468) and SINUS-52 (NCT02898454) studies. Methods: In these randomized, double-blind, placebo-controlled trials, patients received subcutaneous dupilumab 300 mg (n = 438) or placebo (n = 286) every 2 weeks on a background of mometasone furoate nasal spray. Changes from baseline at week 24 in the upper and lower airway outcome measures are reported. Results: Of the 724 patients randomized, 428 (59.1%) had comorbid asthma. In patients with asthma at week 24, dupilumab vs placebo improved the nasal polyp score (−2.04), patient-reported nasal congestion score (−1.04), Lund-Mackay computed tomography scan score (−6.43), peak nasal inspiratory flow (46.15 L/min), and 22-item sinonasal outcome test score (−21.42; all P < .001). The forced expiratory volume in 1 second and 6-item asthma control questionnaire scores were also markedly improved with dupilumab vs placebo. The most common adverse events (nasopharyngitis, headache, injection-site erythema, worsening of nasal polyposis, and asthma) were more frequent with placebo than dupilumab. Conclusion: Dupilumab improved upper and lower airway outcome measures and HRQoL in patients with severe CRSwNP and comorbid asthma and was well tolerated. Trial Registration: ClinicalTrials.gov Identifiers: NCT02912468 (SINUS-24) and NCT02898454 (SINUS-52).