Introduction Mucormycosis, also known as “black fungus”, is a rare and aggressive fungal infection that predominantly affects immunocompromised patients. Mucormycosis is a difficult condition to diagnose, often requiring histological confirmation. Only two previous case reports of mucormycosis infections following caesarean section have been published to date. Case presentation A 24-year-old female from Australia presented with fevers, pain and discharge from her wound site seven days following a lower segment caesarean section. Numerous investigations, including wound swabs and blood cultures remained negative despite clinical evidence of sepsis. The patient failed to improve with broad-spectrum antibiotics and required radical surgical debridement, sacrificing the anterior rectus sheath and external oblique aponeurosis. Tissue samples from the debridement operation found necrotic fibroadipose tissue with fungal hyphae histologically. The hyphae were 90-degree branching with focal angioinvasion, a highly suggestive feature of mucormycosis, which eventually identified Saksenaea vasiformis. The mucormycosis infection was treated with amphotericin B and posaconazole as well as multiple surgical debridement operations. Following resolution of the infection and treatment with vacuum-assisted closure dressings, reconstruction was performed with Phasix™ mesh repair of the abdominal fascia, in addition to biodegradable temporising matrix (BTM) and split-thickness skin grafting. Conclusion This case highlights the exceptionally rare and difficult diagnosis of mucormycosis of a lower segment caesarean section wound, requiring histological diagnostic confirmation. Radical surgical debridement with liposomal amphotericin B with posaconazole was essential for treatment. This case also describes reconstruction of a large abdominal defect and the sacrificed anterior rectus sheath and external oblique aponeurosis in a potentially infected setting in this rare condition.