We report a rare case of severe exudative retinal detachment with orbital granuloma associated with granulomatosis with polyangiitis (GPA). A 42-year-old man developed bilateral conjunctival hyperemia and eye pain 15 months before presenting to us. Because vitreous cells and retinal detachment were detected in his left eye, he was referred to us for further evaluation. The left eye showed scleral edema, cells in the anterior chamber and anterior vitreous, exudative retinal detachment, and elevated white subretinal lesions from the nasal to the inferior parts of the eye fundus. Orbital contrast-enhanced magnetic resonance imaging revealed a granulomatous lesion, retinal detachment, and fluid retention in the left eyeball. Comprehensive rheumatological evaluation revealed proteinase 3 anti-neutrophil cytoplasmic antibody positivity and a history of otitis media, leading to a GPA diagnosis. Methylprednisolone 1,000 mg/day was administered intravenously for 3 days, followed by oral prednisolone and intravenous cyclophosphamide. Although the retinal detachment decreased, scleritis and choroidal detachment relapse were observed in the left eye after the fifth cyclophosphamide administration. After switching from cyclophosphamide to rituximab, the scleritis and choroidal detachment resolved. Remission was successfully maintained with biannual rituximab administration. In this case, we conclude that rituximab was important to re-induce and maintain remission after recurrence. Collaboration with a rheumatologist is essential for proper treatment in related cases. This is the first report of ultra-widefield and multimodal imaging for retinal detachment associated with GPA.