We report results of the final analysis of overall survival (OS) and patient-reported outcomes from the phase III KEYNOTE-585 (ClinicalTrials.gov identifier: NCT03221426) study. Participants with previously untreated, locally advanced, resectable gastric and gastroesophageal junction (G/GEJ) cancer were enrolled into the main (n = 804) and fluorouracil, leucovorin, oxaliplatin, and docetaxel (FLOT; n = 203) cohorts, and randomly assigned 1:1 to neoadjuvant and adjuvant pembrolizumab plus chemotherapy or placebo plus chemotherapy. The primary end points were pathologic complete response (pathCR) by central review, event-free survival (EFS) by investigator, OS, and safety. Patient-reported outcomes was an exploratory end point. After a median follow-up of 59.9 months (range, 39-76), median OS was 71.8 versus 55.7 months (hazard ratio [HR], 0.86 [95% CI, 0.71 to 1.06]) with pembrolizumab plus chemotherapy versus placebo plus chemotherapy in the main cohort. The EFS HR was 0.81 (95% CI, 0.67 to 0.98). Grade ≥3 drug-related adverse event rates were 65% versus 63%. Perioperative pembrolizumab plus chemotherapy did not worsen health-related quality of life versus placebo. Pembrolizumab plus chemotherapy continued to show improved outcomes in pathCR and a trend toward longer EFS versus placebo in the main and main plus FLOT cohorts. Efficacy and safety outcomes with perioperative pembrolizumab plus chemotherapy followed by adjuvant pembrolizumab in participants with untreated, locally advanced resectable G/GEJ cancer were consistent with previous analyses.