Agnes Louise Warner was the daughter of Nancy Robinson and Darius Bingham Warner.

During the United States Civil War, Agnes' father served in the Union Army as a Lieutenant Colonel, Colonel and Brevet General (successively). He was seriously wounded in the Battle of Kennesaw Mountain, resulting in the loss of an arm. In May 1866, he was appointed U.S. Consul in Saint John, New Brunswick, and moved to the city with his wife later that year. Darius held the position of Consul until 1885, when he assumed a partnership in the sawmill and lumber business of his brother: J. R. Warner & Co.

He was warmly remembered as "the man of the hour" following the disastrous fire that swept Saint John in 1877. Telegraphing the news to sources all over the United States, he prompted "instantaneous and hearty response from many quarters," then applied his military experience to the skilful coordination of relief operations. Thirty-seven years later, Agnes would embrace this same spirit of responsibility in the face of international crisis.