Kunishige was the second son of Gikan DATE of the Iwadeyama Date family (a family in the Sendai Domain), and was adopted by Kunizane DATE, the fourteenth head of the Watari Date family.
岩出山伊達家（仙台藩一門）・伊達義監の次男で、亘理伊達家十四代伊達邦実の養子になった。