Nakamasa served Shirakawa-in and Emperor Toba, and was appointed Kebiishi (police and justice chief), Kotaigu no daishin (Senior office secretary of the Empress' quarters), Hyogo no kami (Director of the Bureau of Military Storehouses), and Kokushi (local governor) for Shimousa and Shimotsuke Provinces.
白河院・鳥羽天皇に仕え、検非違使、皇后宮大進、兵庫頭、また下総国、下野国の国司などを歴任。