Importance Preferred neoadjuvant strategies for early or locally advanced triple-negative breast cancer include a 4-drug chemotherapy regimen containing anthracyclines, cyclophosphamide, taxanes, and platinum. Blockade of the programmed death receptor 1/ligand-1 (PD-1/PD-L1) pathway may improve efficacy of classic neoadjuvant chemotherapy. Camrelizumab, an anti-PD-1 antibody, has showed antitumor activity in advanced triple-negative breast cancer. Objective To evaluate the efficacy and adverse events of camrelizumab plus chemotherapy vs placebo plus chemotherapy as neoadjuvant therapy for patients with early or locally advanced triple-negative breast cancer. Design, Setting, and Participants This randomized, double-blind, phase 3 trial enrolled patients from 40 hospitals in China between November 25, 2020, and May 12, 2023 (data cutoff: September 30, 2023). A total of 441 eligible patients were enrolled. Interventions Patients were randomized in a 1:1 ratio to receive either camrelizumab 200 mg (n = 222) or placebo (n = 219) combined with chemotherapy every 2 weeks. The chemotherapy included nab-paclitaxel (100 mg/m(2)) and carboplatin (area under the curve, 1.5) on days 1, 8, and 15 in 28-day cycles for the first 16 weeks followed by epirubicin (90 mg/m(2)) and cyclophosphamide (500 mg/m(2)) every 2 weeks for 8 weeks. Main Outcomes and Measures The primary end point was pathological complete response (defined as no invasive tumor in breast and lymph nodes [ypT0/Tis ypN0]). Results Among 441 females randomized (median age, 48 years), the median (range) follow-up duration from randomization was 14.4 (0.0-31.8) months. Pathological complete response was achieved in 126 patients (56.8% [95% CI, 50.0%-63.4%]) in the camrelizumab-chemotherapy group and 98 patients (44.7% [95% CI, 38.0%-51.6%]) in the placebo-chemotherapy group (rate difference, 12.2% [95% CI, 3.3%-21.2%]; 1-sided P = .004). In the neoadjuvant phase, adverse events of grade 3 or higher occurred in 198 patients (89.2%) in the camrelizumab-chemotherapy group and 182 (83.1%) in the placebo-chemotherapy group; serious adverse events occurred in 77 patients (34.7%) in the camrelizumab-chemotherapy group and 50 (22.8%) in the placebo-chemotherapy group, with fatal adverse events occurring in 2 patients (0.9%) in the camrelizumab-chemotherapy group. Conclusions and Relevance Among patients with early or locally advanced triple-negative breast cancer, the addition of camrelizumab to neoadjuvant chemotherapy significantly improved pathological complete response.