At first, the family reign was supposed to be succeeded by Masanori ROKUGO, the first son of the fifth domain head, Masanaga ROKUGO, however, as Masanori died young in April 1776, Masachika became the heir, and took over as head of the family on January 10, 1784, when his father retired.
はじめは第5代藩主・六郷政長の長男・六郷政展が政林の養嗣子として後を継ぐ予定だったが、政展が安永5年（1776年）3月に早世したために世子となり、天明3年（1783年）12月18日の父の隠居により後を継いだ。