Background: Novel treatments are needed for patients with advanced, triple-negative breast cancer (TNBC) that progresses or recurs after first-line treatment with chemotherapy. The authors report results from the TNBC cohort of the multicohort, open-label, single-arm, phase 2 LEAP-005 study of lenvatinib plus pembrolizumab in patients with advanced solid tumors (ClinicalTrials.gov identifier NCT03797326). Methods: Eligible patients had metastatic or unresectable TNBC with disease progression after one or two lines of therapy. Patients received lenvatinib (20 mg daily) plus pembrolizumab (200 mg every 3 weeks; up to 35 cycles). The primary end points were the objective response rate according to Response Evaluation Criteria in Solid Tumors, version 1.1, and safety (adverse events graded by the National Cancer Institute's Common Terminology Criteria for Adverse Events, version 4.0). Duration of response, progression-free survival, and overall survival were secondary end points. Results: Thirty-one patients were enrolled. The objective response rate by investigator assessment was 23% (95% confidence interval [CI], 10%-41%). Overall, the objective response rate by blinded independent central review (BICR) was 32% (95% CI, 17%-51%); and, in patients who had programmed cell death ligand 1 combined positive scores >= 10 (n = 8) and <10 (n = 22), the objective response rate was 50% (95% CI, 16%-84%) and 27% (95% CI, 11%-50%), respectively. The median duration of response by BICR was 12.1 months (range, from 3.0+ to 37.9+ months). The median progression-free survival by BICR was 5.1 months (95% CI, 1.9-11.8 months) and the median overall survival was 11.4 months (95% CI, 4.1-21.7 months). Treatment-related adverse events occurred in 94% of patients (grade 3, 52%; grade 4, 0%). One patient died due to a treatment-related adverse event of subarachnoid hemorrhage. Conclusions: The combination of lenvatinib plus pembrolizumab demonstrated antitumor activity with a manageable safety profile in patients with previously treated, advanced TNBC.