Bull was born in North Bay, Ontario, to George L.T. and Gertrude Isabelle LaBrosse Bull. George Bull was from a family from the Trenton area and had moved to North Bay in 1903 to start a law firm. As a Catholic, LaBrosse would have been forbidden from marrying Bull, as he was Anglican. Bull converted to Catholicism on February 20, 1909, and the two married three days later. Over the next few years the couple had 10 children: Bernice Gwendolyn Florence, Henry, Philis, Charles Esmond, Clyde, Vivian, Ronald, Frank, Gerald, and Gordon.