Herpes simplex virus uveitis without corneal reactivation is more frequent than previously thought. Although herpes simplex virus has been implicated as a cause of postoperative uveitis and endophthalmitis, it has not been reported as a cause of acute postoperative endophthalmitis within the early postoperative period, specifically within one week following cataract extraction. A 55-year-old man with vascularized irregular central disc-shaped stromal corneal opacity with complicated cataracts underwent cataract surgery. Intraoperatively, there was posterior capsular rent, requiring anterior vitrectomy. On postoperative day three, the patient had an increase in inflammation in the anterior chamber (grade 4+) with marked vitreous haze (grade 4). Vitreous taps were negative for bacteria and fungi, and despite intravitreal injections of vancomycin and ceftazidime, the patient had worsening of inflammation with increasing exudates and the appearance of the fibrinous membrane in the anterior chamber. Polymerase chain reaction (PCR) of aqueous and vitreous samples at this point of time yielded positive serology for herpes viral DNA, and the patient was started on oral valacyclovir. The ocular inflammation resolved soon after switching to oral valacyclovir. Typical acute postoperative endophthalmitis starts two to seven days after surgery, and the most common isolate in vitreous biopsies is coagulase-negative staphylococci. We report a rare case of acute-onset herpetic endophthalmitis presenting within 72 hours following cataract surgery for a complicated cataract in a patient with a history of pre-existing healed viral keratitis. Our case highlights that a suspicion of viral endophthalmitis should be kept in mind as a cause of acute-onset post-cataract surgery endophthalmitis, especially in cases of surgery that fail to yield a positive result on Gram’s stain, culture or PCR for bacteria and fungi.