Power was born in Knockbrit,
Kingdom of Ireland, to Edmund Power and Ellen Sheehy. His father was a landowner and the sometime editor of the
Clonmel Gazette. His mother was the daughter of Edmund Sheehy, who was executed as an accessory to
Nicholas Sheehy, his cousin. He was the brother of the
Marguerite Gardiner, the Countess of Blessington, a novelist, biographer and a literary hostess. His granddaughter
Marguerite Helen Power was named for his sister. == Military career ==