Aims Sinonasal metastases from cutaneous melanoma are exceptionally rare and may present with nonspecific sinonasal or orbital symptoms. Orbital involvement in this context is even less common. We present a rare case of orbital cellulitis secondary to metastatic melanoma involving the maxillary sinus and discuss diagnostic and management considerations. Methods A 54-year-old female with a history of Stage IIIC BRAF V600E-positive melanoma presented with three weeks of nasal congestion and maxillary pain, followed by two days of left periorbital swelling. She was afebrile with no visual symptoms. Examination revealed Chandler Stage II sinogenic orbital cellulitis without proptosis or ophthalmoplegia. CT imaging demonstrated full opacification of the left maxillary sinus with orbital cellulitis. The patient failed to improve on intravenous antibiotics and underwent urgent functional endoscopic sinus surgery (FESS). Results Intraoperatively, black necrotic debris was identified within the left maxillary sinus. Histopathology demonstrated a malignant epithelioid neoplasm. Immunohistochemistry was positive for SOX10, S100, and BRAF V600E mutation, confirming metastatic melanoma. This represented the first recurrence detected since a surveillance PET scan six months earlier had shown no active disease. Conclusions This case illustrates the importance of maintaining a high index of suspicion for malignant causes in atypical sinusitis or orbital cellulitis presentations, particularly in patients with prior melanoma or immunocompromise. Metastatic melanoma, though rare in the sinonasal tract, can mimic infective or inflammatory pathology. Early surgical intervention can facilitate both diagnostic confirmation and symptomatic relief, underscoring the role of FESS not only in source control but also in uncovering occult malignancy.