Evidence from real-world clinical settings is lacking with regard to first-line immunotherapy plus chemotherapy for the treatment of non-small cell lung cancer (NSCLC). Our aim was to describe outcomes for patients treated with first-line pembrolizumab-combination therapy for metastatic nonsquamous NSCLC in US oncology practices. Using an anonymized, nationwide electronic health record-derived database, we identified patients who initiated pembrolizumab plus pemetrexed-carboplatin in the first-line setting (May 2017 to August 2018) after diagnosis of metastatic nonsquamous NSCLC that tested negative for EGFR and ALK genomic aberrations. Eligible patients had ECOG performance status of 0-1. An enhanced manual chart review was used to collect outcome information. Time-to-event analyses were performed using the Kaplan-Meier method. Of 283 eligible patients, 168 (59%) were male; median age was 66 years (range 33-84); and the proportions of patients with PD-L1 tumor proportion score (TPS) of ≥ 50%, 1-49%, < 1%, and unknown were 28%, 27%, 28%, and 17%, respectively. At data cutoff on August 31, 2019, median patient follow-up was 20.3 months (range 12-28 months), and median real-world times on treatment (rwToT) with pembrolizumab and pemetrexed were 5.6 (95% CI 4.5-6.4) and 2.8 months (95% CI 2.2-3.5), respectively. Median overall survival (OS) was 16.5 months (95% CI 13.2-20.6); estimated 12-month survival was 59.5% (95% CI 53.3-65.0); rwProgression-free survival was 6.4 months (95% CI 5.4-7.8); and rwTumor response rate (complete or partial response) was 56.5% (95% CI 50.5-62.4). Median OS was 20.6, 16.3, 13.2, and 13.7 months for patient cohorts with PD-L1 TPS ≥ 50%, 1-49%, < 1%, and unknown, respectively. These findings demonstrate the effectiveness of pembrolizumab plus pemetrexed-carboplatin by describing clinical outcomes among patients with metastatic nonsquamous NSCLC who were treated at US oncology practices.