Jack MacDonald was born in 1902 to a family of farmers and lobstermen in River John Nova Scotia. The MacDonald family had already been there a long time, having immigrated from the Scottish Highlands in the early 1800s. Jack's father, Alexander MacDonald owned a large plot of land and a farmhouse that had been in the family for many generations. Jack attended school into his teenage years but never graduated from high school.

Jack and his brothers had many jobs depending on the season. All of his siblings would have worked on the farm doing small chores from the time they were children. As they got older (and stopped going to school) this role would have grown to include most of the farm labor. They also would have spent much of the summer on the lobster boat making extra money. Similarly in the winter, Jack worked all kinds of odd jobs around town to help support the family.