Yokosuka Domain
Nishio Tadayuki was the second son of the third daimyō of Yokosuka Domain, Nishio Tadamitsu. As his elder brother Tadamasa died in October 1765, Tadayuki was chosen to succeed his father. In 1766 he received court rank and "Yamashiro no Kami". In 1782, he succeeded his newly retired father as daimyō of the Yokosuka Domain, also receiving his father's courtesy title of "Oki no Kami".