Matsudaira Masayasu served as a bushō during the Sengoku period.

Masayasu served as the third head of the Ōkusa-Matsudaira family based in the Ōkusa township in the Nukata District of Mikawa Province.  The Ōkusa-Matsudiara were founded by Matsudaira Mitsushige, the fifth son of Matsudaira Nobumitsu of the Iwatsu-Matsudaira.  Mitsushige was based at Okazaki Castle.  Until 1524, when Okazaki Castle was captured by Matsudaira Kiyoyasu, the Ōkusa-Matsudaira were called the Okazaki-Matsudaira.

In a copy of a historical record that appears to have been written by him, he is referred to as Nobusada.

Masayasu is generally surmised to have been the son of Mitsushige, but his real father is also noted as Saigō Danjō-zaemon Yoritsugu.  Therefore, he is also called Saigō Nobusada.

He succeeded his older brother, Matsudaira Chikasada, to become the third head of the clan based at Okazaki Castle, governing the area in the southern portion of present-day Okazaki and Ōkusa Castle.

In 1524, Masayasu incurred an attack by Matsudaira Kiyoyasu at Yamanaka Castle (an outlying castle), after which he turned-over Okazaki Castle and his landholdings.  The capture of Yamanaka Castle was based on a plan devised by a retainer of Kiyoyasu named Ōkubo Tadashige.

In addition to relinquishing Okazaki, he had his daughter, Oharu, wed Kiyoyasu and then retired to Ōkusa.  His grave is at the Dairin Temple in Okazaki.