Nakayama Katsumasa served as a bushō during the Sengoku period. Katsumasa was a retainer of the Uragami clan, holding the Court title of Governor of Bitchū. Earlier referred to as Nobumasa, the name of Katsumasa was confirmed based on his signature and seal on a letter from Nakayama Bitchū-no-kami addressed to Saisho Buzen-no-kami Hisatsune.
Amidst a sibling rivalry between Uragami Masamune and Uragami Munekage, Katsumasa constructed and resided in Numa Castle (also known as Kameyama Castle) in Bizen. Following their reconciliation, Katsumasa, along with Shimamura Moritsura, were killed by Ukita Naoie between 8/29 of 1559 and the end of 1562. This likely owed to the view held by Munekage that Katsumasa and Moritsura were impediments to his plan to acquire complete control of Bizen.
According to unauthenticated accounts, Katsumasa had his daughter wed Ukita Naoie to avoid being targeted by Naoie. Instead, in furtherance of the plans by the Uragami to garner control of Bizen, Naoie accused Katsumasa of plotting a rebellion and was then killed in 1559. Following his demise, his territory was seized by Naoie, but this shifted responsibility to Naoie for the assassination in the midst of a broader effort by the Uragami to eliminate forces aligned with the Mōri.