A woman in her 70s experienced painless vision loss in the right eye for 1 month. Acute retinal necrosis-induced panuveitis was the referral diagnosis. With dense vitreous haze, a vitrectomy was performed for vitreous biopsy followed by multimodal imaging. Vitreous biopsy yielded negative PCR results for herpes viruses and only inflammatory cells. Post-vitrectomy imaging showed involuted but pervasive pigmentary foci in the outer retina and the retinal pigment epithelium. Concurrently, peripheral blood showed pancytosis with giant platelets and a Janus kinase 2 (JAK2) mutation, which prompted a haematological evaluation. CT and MRI revealed a right frontal lobe intra-axial mass, diagnosed as diffuse large B cell lymphoma (DLBCL). Subsequently, bone marrow aspirate confirmed the pathogenic V617F JAK2 mutation. Following chemotherapy, the patient achieved lymphoma regression and uveitic quiescence. This is the first case report of acute unilateral panuveitis in a patient with JAK2 mutation and DLBCL but without evidence of intraocular involvement.