Chemotherapy remains a standard treatment option for metastatic triple-negative breast cancer (TNBC) but is associated with limited survival. Although some targeted antibody-drug conjugates have demonstrated clinical benefits and are considered standard therapy, persistent unmet medical needs remain due to varying accessibility. The OptiTROP-Breast01 phase 3 trial assessed sacituzumab tirumotecan (sac-TMT) versus chemotherapy in patients with locally recurrent or metastatic TNBC who had received two or more prior therapies, including at least one for metastatic disease. Patients were randomized to sac-TMT (n = 130) or chemotherapy (n = 133). The primary endpoint of progression-free survival (PFS) by blinded independent central review (BICR) was met based on the protocol-specified interim analysis. At final analysis, the median PFS by BICR was 6.7 (95% confidence interval (CI), 5.5-8.0) months with sac-TMT and 2.5 (95% CI, 1.7-2.7) months with chemotherapy (hazard ratio (HR), 0.32; 95% CI, 0.24-0.44; P < 0.00001). Concurrently, at the protocol-specified interim analysis for overall survival (OS), the median OS was not reached (95% CI, 11.2 months to not estimable (NE)) with sac-TMT and 9.4 (95% CI, 8.5-11.7) months with chemotherapy (HR, 0.53; 95% CI, 0.36-0.78; P = 0.0005). The percentage of patients with an objective response was 45.4% with sac-TMT and 12.0% with chemotherapy. The median duration of response was 7.1 (95% CI, 5.6-NE) months with sac-TMT and 3.0 (95% CI, 2.5-NE) months with chemotherapy. The most common treatment-related adverse event with sac-TMT was hematologic toxicity. Sac-TMT demonstrated statistically significant and clinically meaningful improvements in PFS compared to chemotherapy, with a manageable safety profile. The study findings support sac-TMT as an additional effective treatment option for pretreated metastatic TNBC. ClinicalTrials.gov identifier: NCT05347134.