Treatment during acute or early human immunodeficiency virus (HIV)-1 infection is associated with immunologic and virologic benefits. To evaluate darunavir/cobicistat/emtricitabine/tenofovir alafenamide (D/C/F/TAF) efficacy/safety among patients with acute or early HIV-1 infection who rapidly initiate treatment. DIAMOND (ClinicalTrials.gov Identifier: NCT03227861), a phase 3 study, evaluated the efficacy/safety of D/C/F/TAF 800/150/200/10 mg in rapid initiation. Adults aged ≥18 years began D/C/F/TAF within 14 days of diagnosis, prior to the availability of screening/baseline laboratory results. In this subgroup analysis, virologic response (HIV-1 RNA <50 copies/mL) was assessed at Week 48 by intent-to-treat FDA snapshot (ITT-FDA snapshot) and observed (excluding patients with missing data) analyses in patients with acute (HIV-1 antibody negative and HIV-1 RNA positive/p24 positive) or early (HIV-1 antibody positive and suspected infection ≤6 months before screening/baseline) infection. Among 109 patients, 13 had acute and 43 had early HIV-1 infection. High rates of virologic response were demonstrated at Week 48 by ITT-FDA snapshot (acute: 10/13 [76.9%]; early: 37/43 [86.0%]) and observed (acute: 10/11 [90.9%]; early: 37/38 [97.4%]) analyses. No patients discontinued or required regimen change due to baseline resistance or lack of efficacy, or developed protocol-defined virologic failure. Through Week 48, 7 (53.8%) acute and 22 (51.2%) early infection patients had a D/C/F/TAF-related adverse event (AE); none had a D/C/F/TAF-related grade 4 or serious AE. High rates of viral suppression during acute/early infection were achieved with D/C/F/TAF rapid initiation, no treatment-emergent resistant mutations were observed, and D/C/F/TAF was safe and well tolerated.