Background: Immune-related adverse events (irAEs) have been associated with improved outcomes in different tumors; however, their impact during neoadjuvant immune checkpoint inhibitor therapy and chemotherapy in triple-negative breast cancer (TNBC) remains unknown. Patients and methods: This analysis included patients from a phase I/II single-arm clinical trial at Yale Cancer Center and its regional care centers. The study was conducted from December 2015 to December 2020. Eligible patients were adults aged ≥18 years with clinical stage I-III TNBC for whom systemic chemotherapy was indicated. Patients received durvalumab concomitant with nab-paclitaxel and dose-dense doxorubicin–cyclophosphamide. Durvalumab was not administered post-operatively. We examined the association of developing an irAE with pathologic complete response (pCR = ypT0/is, ypN0), residual cancer burden (RCB), event-free survival (EFS), and overall survival (OS). A landmark analysis from the time of surgery was also carried out. Results: A total of 67 patients were eligible for toxicity and efficacy analysis; of these, 27 had irAEs of any grade and 13 had multiple irAEs. The median follow-up was 61 months (range 6.8-94.03 months). The most frequent irAEs were dermatologic (n = 14), endocrine (n = 13), and gastrointestinal (n = 5). Patients who experienced irAEs achieved a pCR or RCB 0-1 rate of 56% and 73%, respectively, compared with 40% and 55% in those without irAEs (P = 0.309 and 0.19). Development of irAE was also associated with significantly improved EFS [hazard ratio (HR) 0.25; 95% confidence interval (CI) 0.09-0.66, P = 0.024] and a trend for improved OS (HR 0.42; 95% CI 0.14-1.27, P = 0.17). Patients with more than one irAE had no EFS events. The landmark analysis showed similar results (EFS HR 0.19, P = 0.014; OS HR 0.4, P = 0.16). Conclusions: The development of irAE was associated with numerically improved pCR rates, lower RCB, and significantly higher EFS in patients treated with neoadjuvant immune checkpoint therapy plus chemotherapy.