Azacitidine plus venetoclax is a standard of care for patients with newly diagnosed AML who are unfit for intensive chemotherapy. However, mutations are a common mechanism of resistance to this regimen. The addition of gilteritinib, an oral FLT3 inhibitor, to azacitidine and venetoclax may improve outcomes in patients with -mutated AML. This phase I/II study evaluated azacitidine, venetoclax, and gilteritinib in two cohorts: patients with (1) newly diagnosed -mutated AML who were unfit for intensive chemotherapy or (2) relapsed/refractory -mutated AML (ClinicalTrials.gov identifier: NCT04140487). The primary end points were the maximum tolerated dose of gilteritinib (phase I) and the combined complete remission (CR)/CR with incomplete hematologic recovery (CRi) rate (phase II). Fifty-two patients were enrolled (frontline n = 30; relapsed/refractory n = 22). The recommended phase II dose was gilteritinib 80 mg once daily in combination with azacitidine and venetoclax. In the frontline cohort, the median age was 71 years and 73% of patients had an -internal tandem duplication (ITD) mutation. The CR/CRi rate was 96% (CR, 90%; CRi, 6%). Sixty-five percent of evaluable patients achieved -ITD measurable residual disease <5 × 10 within four cycles. With a median follow-up of 19.3 months, the median relapse-free survival (RFS) and overall survival (OS) have not been reached and the 18-month RFS and OS rates are 71% and 72%, respectively. In the relapsed/refractory cohort, the CR/CRi rate was 27%; nine additional patients (41%) achieved a morphologic leukemia-free state. The most common grade 3 or higher nonhematologic adverse events were infection (62%) and febrile neutropenia (38%), which were more frequent in the relapsed/refractory cohort. The combination of azacitidine, venetoclax, and gilteritinib resulted in high rates of CR/CRi, deep molecular responses, and encouraging survival in newly diagnosed -mutated AML. Myelosuppression was manageable with mitigative dosing strategies.