Background: Plasmacytomas are monoclonal proliferations of plasma cells occurring in bone or soft tissue without systemic involvement. Solitary bone plasmacytoma (SBP) is a localized tumor without other skeletal lesions or bone marrow infiltration. Clival involvement is extremely rare, with few cases reported. Case Report: A 47-year-old male presented with a 3-month history of diplopia. MRI revealed a T1- and T2-isointense clival lesion with bone destruction. Endoscopic transnasal transsphenoidal biopsy confirmed plasmacytoma. Systemic workup ruled out multiple myeloma. The patient received 50 Gy radiotherapy in 25 fractions. At 14-month follow-up, he showed complete clinical recovery and reduction in tumor size. Conclusion: Solitary clival plasmacytoma is a rare but treatable cause of isolated diplopia. It should be considered in the differential diagnosis of clival lesions, with radiotherapy offering favourable outcomes.