On May 21, 1678, due to the death of his father, Nagatsugu, Nagashige's elder brother, Nagasuke OGASAWARA succeeded their father as the head of the family and became the lord of the Yoshida Domain in Mikawa Province.
延宝6年(1678年)3月31日には、父長矩の死去で長重の兄の小笠原長祐が家督を相続し三河吉田藩主となっている。