In 1773, the former lord of the domain and his older brother Masahiro INABA died young without an heir, and Masanobu succeeded him by becoming the adopted heir.
安永2年（1773年）、先代藩主で兄だった稲葉正弘が嗣子無くして若死にしたため、その養嗣子となって後を継いだ。